Even though the pandemic is ongoing, our underlying revenue growth of 6% is the highest in over 6 years and accelerated sequentially across every business.
We also grew adjusted earnings per share by 21% and generated significant margin expansion.
With 6% underlying growth to begin the year, we now expect full year 2021 underlying revenue growth to be at the high end of our 3% to 5% guidance range and possibly above.
PayneWest was one of the largest independent agencies in the U.S. with more than 700 employees in 26 locations.
We also strengthened our commitment to a better sustainable future through our pledge to be carbon-neutral this year along with the commitment to reduce our carbon emissions by 15% by 2025.
The Marsh Global Insurance Market Index showed price increases of 18% year-over-year versus 22% in the fourth quarter.
The pace of price increases moderated sequentially in the first quarter after accelerating for 11 straight quarters.
However, the 18% increase is still one of the highest since we started publishing the index in 2012.
Global property insurance was up 15% and global financial and professional lines were up 40% while global casualty rates were up 6% on average and U.S. workers compensation rates were modestly negative.
Turning to reinsurance, the Guy Carpenter's Global Property Catastrophe Rate on Line index increased just under 5% at the January 1st reinsurance renewals.
We generated adjusted earnings per share of $1.99, which is up 21% versus a year ago, driven by a combination of strong growth and the continuation of the suppressed environment for travel and entertainment expenses as we continue to operate largely remotely.
Total revenue increased 9% versus a year ago, and rose 6% on an underlying basis.
Underlying revenue grew 7% in IRS, and 3% in consulting.
Marsh grew 8% in the quarter on an underlying basis, the highest quarterly underlying growth since 2003, and benefited from double-digit new business growth.
Guy Carpenter grew 7% on an underlying basis in the quarter.
Oliver Wyman underlying revenue grew by 11% as demand accelerated.
Overall, the first quarter saw adjusted operating income growth of 20%, and our adjusted operating margin expanded 250 basis points year-over-year, reflecting positive operating leverage and favorable expense comparisons.
As we mentioned, we now expect 2021 underlying revenue growth to be at the high end of our 3% to 5% range, and possibly above.
One company with 4 global businesses, united by a shared purpose to make a difference in the moments that matter.
Consolidated revenue increased 9% in the first quarter to $5.1 billion, reflecting underlying growth of 6%.
Operating income and adjusted operating income were both approximately $1.4 billion.
Our adjusted operating margin increased 260 basis points to 29.6%.
GAAP earnings per share was $1.91, and adjusted earnings per share was $1.99, up 21% compared with the first quarter a year ago.
First quarter revenue was $3.2 billion, up 11% compared with a year ago, or 7% on an underlying basis.
Adjusted operating income increased 17% to $1.1 billion, and our adjusted operating margin expanded 210 basis points to 36.6%.
At Marsh, revenue in the quarter was $2.3 billion, up 13% compared with a year ago, or 8% on an underlying basis.
This was Marsh's highest level of underlying growth in nearly 2 decades.
The U.S. and Canada division delivered another exceptional quarter with underlying revenue growth of 9%.
And they have now averaged 6% underlying growth over the last 12 quarters.
In international, underlying growth was strong at 6%, marking the highest underlying growth since 2013.
EMEA was up 6% with strong results in each region, including in the UK.
Asia Pacific was up 8%, a strong rebound from the fourth quarter, and comes on top with 6% growth in the first quarter of 2020.
And Latin America grew 6% on an underlying basis, continuing to show sequential improvement.
Guy Carpenter's revenue was $895 million, up 8% or 7% on an underlying basis, driven by strong growth in North America, EMEA, Global Specialties and Latin America treaty.
Guy Carpenter has now achieved 5% or higher underlying growth in 12 of the last 14 quarters.
In the Consulting segment, revenue in the quarter was $1.9 billion, up 6% from a year ago, or 3% on an underlying basis.
Adjusted operating income was $370 million, and the adjusted operating margin expanded by 330 basis points to 20.5%.
At Mercer, revenue in the quarter was $1.3 billion, which was flat on an underlying basis.
Wealth increased 1% on an underlying basis, reflecting strong growth in investment management, offset by a modest decline in defined benefits.
Our assets under delegated management grew to approximately $380 billion at the end of the first quarter, up 42% year-over-year, or 6% sequentially, benefiting from net new inflows and market gains.
Health underlying revenue was flat in the quarter, but faced a tough comparison to 8% growth in the first quarter of last year.
And Career grew 1% on an underlying basis, reflecting strong sequential improvement.
At Oliver Wyman, revenue in the quarter was $585 million, an increase of 11% on an underlying basis.
Adjusted corporate expense was $57 million in the quarter.
Foreign exchange added approximately $0.06 to our adjusted EPS.
Our other net benefit credit was $71 million in the quarter.
Investment income was $11 million in the first quarter on a GAAP basis, or $10 million on an adjusted basis, and mainly reflects gains in our private equity portfolio.
Interest expense in the first quarter was $118 million compared to $127 million in the first quarter of 2020, reflecting lower debt levels in the period.
Based on our current forecast, we expect approximately $114 million of interest expense in the second quarter.
Our effective adjusted tax rate in the first quarter was 24.3% compared to 23.2% in the first quarter of last year.
Excluding discrete items, our effective adjusted tax rate was approximately 25.5%.
, it is reasonable to assume a tax rate between 25% and 26% for 2021.
Our current outlook for 2021 assumes the global economy returns to growth in the second quarter, with a strong recovery in the U.S. Based on this outlook and our strong first quarter performance, we now expect underlying revenue growth to be at the high end of our 3% to 5% underlying growth guidance, and possibly above.
We ended the quarter with $11.3 billion of total debt, which was consistent with the level at December 31st.
In April, we repaid $500 million of senior notes scheduled to mature in July, taking advantage of a prepayment option.
This repayment brought our debt down to $10.8 billion and completed our planned deleveraging, marking an important milestone for us.
Our next scheduled debt maturity is in January 2022 when $500 million of senior notes will mature.
Under this new facility, we increased the credit available to $2.8 billion from $1.8 billion.
In addition, we increased the size of our commercial paper program and now have capacity to issue $2 billion, up from $1.5 billion previously.
We repurchased 1 million shares of our stock for $112 million.
We continue to expect to deploy approximately $3.5 billion of capital in 2021 across dividends, debt reduction, acquisitions and share repurchases.
Our cash position at the end of the first quarter was $1.1 billion.
Uses of cash in the quarter totaled $392 million and included $237 million for dividends, $112 million for share repurchases and $43 million for acquisitions.

Summary:
We generated adjusted earnings per share of $1.99, which is up 21% versus a year ago, driven by a combination of strong growth and the continuation of the suppressed environment for travel and entertainment expenses as we continue to operate largely remotely.
Consolidated revenue increased 9% in the first quarter to $5.1 billion, reflecting underlying growth of 6%.
GAAP earnings per share was $1.91, and adjusted earnings per share was $1.99, up 21% compared with the first quarter a year ago.