Revenue growth of 8% and increase in adjusted diluted earnings per share of 15% highlighted the robust demand for our best-in-class integrated risk assessment offerings.
Additionally, we've raised our adjusted diluted earnings per share guidance to be in the range of $11.55 to $11.85.
MIS revenue grew 4%.
That's despite the tough prior year comparable, while MA achieved its highest ever quarterly revenue, up 15% from last year.
On an organic constant currency basis, MA revenue increased 8%.
Moody's adjusted operating income rose 12% to $861 million, and the adjusted operating margin expanded 200 basis points to 55.4%.
Adjusted diluted earnings per share was $3.22, up 15%.
Although overall issuance declined by 16%, as you can see on the chart, second quarter issuance was still well above the historical 10-year average as shown on the blue line.
And in the second quarter, transactional MIS revenue grew 3%, while MIS rated issuance declined 16%.
And you can see that issuance was down 68% in the second quarter versus the prior year.
However, leveraged loans, which has a greater proportion of issuers on per issuance or pay-as-you-go commercial programs, represented by the dark blue bubble on the far right, saw issuance up over 200%.
Our emphasis on renewable sales has increased the proportion of recurring revenue by four percentage points in the trailing 12-month period to 92%.
Our industry-leading product offerings and solutions leverage information on hundreds of millions of entities and ownership structures as well as detailed profiles on over 13 million politically exposed individuals.
We further expanded our capabilities to include asset and liability management and balance sheet solutions, portfolio analytics and other tools to help address new accounting standards such as IFRS 17 and CECL.
Together, this has contributed to our ability to deliver 20% organic revenue growth over the trailing 12 months in this segment.
This offering combines Moody's ESG scoring methodology with company-specific data and predictive analytics to produce ESG scores for over 140 million small- and medium-sized enterprises.
And since 2012, we provided hundreds of second-party opinions across 30 countries with over 60 second-party opinions provided just in the first half of this year.
I'm pleased that we ranked number two on Chartis' STORM Top 50, demonstrating our position at the forefront of digital transformation in our sector.
I'm also enormously proud that Moody's was named a Top 50 Company for Diversity by DiversityInc.
And finally, I'm thrilled that Moody's joined the Fortune 500 earlier this quarter.
In the second quarter, MIS revenue increased 4%, supported by a 3% rise in transaction revenue, while global MIS rated issuance declined 16%.
As a result of favorable mix, corporate finance revenue declined 4% versus a 26% decrease in issuance.
Financial institutions revenue rose 6%, above the 1% increase in issuance.
Revenue from public, project and infrastructure finance declined 2% compared to a 45% decrease in issuance as increased non-U.S. project and infrastructure activity was offset by a reduction in U.S. infrastructure supply.
Structured finance revenue increased 73%, supported by an over 200% growth in issuance.
This is due to approximately 200 CLO deals this quarter, our highest on record, predominantly attributable to refinancing activity.
MIS' adjusted operating margin expanded 230 basis points to 66.3%.
Second quarter revenue rose 15% or 13% on an organic basis.
In RD&A, revenue increased 19% or 16% on an organic basis.
For ERS, recurring revenue rose 16%, driving overall ERS growth of 5% or 3% organically.
This reflected the demand for our insurance and asset management offerings, tools supporting upcoming accounting standards implementations such as IFRS 17 as well as our SaaS-based credit assessment and origination solutions.
Additionally, ERS' recurring revenue comprised 88% of second quarter revenue, up eight percentage points from the prior year period.
MA's adjusted operating margin expanded 310 basis points to 31.8%.
Our full year 2021 guidance is underpinned by the following macro assumptions: a rise in the 2021 U.S. and euro area GDP to a range of 6% to 7% and 4% to 5%, respectively; benchmark interest rates will remain low, with U.S. high-yield spreads remaining below approximately 500 basis points; the U.S. unemployment rate will decline to under 5% by year-end; and the global high-yield default rate will fall below 2% by year-end.
Specifically, our forecast for the balance of 2021 reflects U.S. exchange rates for the British pound of $1.38 and $1.19 for the euro.
Given our improved revenue outlook and expense stability, we now project Moody's adjusted operating margin to be approximately 51%.
We raised the diluted and adjusted diluted earnings per share guidance ranges to $10.95 to $11.25 and $11.55 to $11.85, respectively.
We increased our free cash flow forecast to be between $2.2 billion and $2.3 billion.
And we anticipate full year share repurchases to remain at approximately $1.5 billion subject to available cash, market conditions and other ongoing capital allocation.
We are raising our issuance forecast for leveraged loans to be up approximately 75% and for high-yield bonds to be up approximately 25%.
These are meaningful increases compared to our prior outlook of up 55% and approximately flat, respectively, and is the result of better-than-expected second quarter issuance as well as ongoing favorable refinancing conditions and heightened M&A activity.
We expect that the increase in leveraged loan supply will continue to drive CLO creation and are therefore also improving the structured issuance outlook to be up approximately 75%.
Following a very active 2020, full year investment-grade supply is now forecast to decrease by approximately 40%.
That's slightly lower than our previous guidance, which anticipated volumes to decline 30%.
Also, after a surge in activity in the second quarter, we are increasing our guidance for new mandates to be in the range of 950 to 1,050.
MIS' adjusted operating margin guidance remains at approximately 61% as our improved top line outlook is partially offset by higher incentive compensation accruals and an acceleration in ESG, technology and automation investments in the second half of the year.
We are raising MA's adjusted operating margin guidance to be in the range of 30% to 31% as we continue to effectively manage our expense base while accelerating strategic investment back into the business.

Summary:
Adjusted diluted earnings per share was $3.22, up 15%.