During the fourth quarter, we increased the accrual related to this matter to $8 million for a potential settlement.
I'm also pleased to note that we again realized a very strong performance in our termite service line, posting year-over-year double-digit growth of 14.3%.
To be more specific, termite damage claims received have declined from a high of 9,349 to the low of 380 new claims received this past year while, at the same time, revenue from termite has tripled.
Q4 revenues increased 11.9% to $600.3 million, compared to $536.3 million the previous year.
Net income rose to $65.3 million or $0.13 per diluted share, compared to $62.6 million or $0.13 per diluted share for the same period in 2020.
Our revenues for the full year were $2.424 billion, an increase of 12%, compared to $2.161 billion for the same period last year.
Net income for the full year increased 34.5% to $350.7 million or $0.71 per diluted share, compared to $260.8 million or $0.53 per diluted share for the comparable period last year.
All our business lines experienced solid growth, with residential pest control up 11.9% and termite realizing growth of 13.6%.
Additionally, commercial pest control delivered an impressive 11.4% growth over the fourth quarter of last year.
The sales payroll expense trend is reflective of the planned investment we made in up-staffing our residential and commercial sales teams over the last 12 months.
Last week, we held our virtual Rollins leadership meeting with over 175 of our top leaders.
Compared to Q4 of 2020, our fuel costs were up 56.5% in Q4 of 2021.
That equated to over $4.5 million in increased fuel costs for the quarter.
Due to concerns about these types of cybersecurity issues, in Q4, we fast-tracked our multiyear strategy to enhance our protection against cybersecurity threats by accelerating a $3 million expenditure.
Last year ended strong with over 70% of our trailing 12 months revenue acquired occurring in the fourth quarter.
Our fourth-quarter revenues of $600 million was an increase of 11.9% actual exchange rate growth, 8.9% organic.
For the constant exchange rate, the total revenue growth percentages calculated to 11% with an 8.1% organic.
For the full year 2021, revenues of $2.4 billion was an increase of 12.2% over full year 2020, 9.5% organic.
The constant exchange rate, total revenue growth for 2021 equaled 11.4%, 8.7% organic.
For the fourth quarter growth over last year, residential grew 11.9%, 8.4% organic; commercial grew 11.4%, 9.3% organic; lastly, we have termite, which grew 13.6% with 10.1% organic.
For the full year 2021 over 2020, residential grew 12.9%, 10% organic; commercial grew 10.2%, 7.4% organic; and we closed out with termite at a 14.3% growth, 11.9% organic.
Fourth-quarter adjusted 2021 EBITDA was $122.2 million or 11.2% over 2020.
Fourth quarter 2021 adjusted earnings per share was $0.14 per diluted share or 7.7% improvement over 2020.
For the full year 2021, our adjusted EBITDA was $546.4 million or 20.1% over last year.
Year to date, 2021 adjusted earnings per share was $0.68 per diluted share or 25.9% over 2020.
For fourth quarter 2021, gross margin increased 50.4% or 0.10 point over last year.
That was after overcoming our strong headwinds of fleet expenses, specifically fuel in the amount of $4.5 million and termite M&F for $2.7 million.
Sales, general and administrative fourth quarter 2021 margin increased 1.6% over last year.
Related to the SEC potential settlement, we recorded an accrual of $5 million in Q4.
This was in addition to the $3 million we previously accrued in the third quarter.
Our dividends full year 2021 were $208.7 million or an increase of 30% over 2020, while cash used for acquisitions declined 5.8% to $139 million for 2021.
We ended the current period with $105.3 million in cash, of which $78.1 million was held by our foreign subsidiaries.
For the fourth quarter of 2021, our free cash flow was $88.9 million, or a decrease of 0.8% over last year.
Full-year free cash flow was $395 million or a decrease of $41 million.
This decline was primarily due to the $30 million 2020 carry back taxes paid in 2021 and a $32 million gain from the sale of the Clark properties, the latter of which is an operating cash reconciling item.
Last, I'm happy to share that yesterday our board of directors approved a regular cash dividend of $0.10 per share that will be paid on March 10, 2022, to shareholders of record at the close of business, February 10, 2022.
This represents a 25% increase over the March 2021 regular cash dividend paid out.

Summary:
Q4 revenues increased 11.9% to $600.3 million, compared to $536.3 million the previous year.
Net income rose to $65.3 million or $0.13 per diluted share, compared to $62.6 million or $0.13 per diluted share for the same period in 2020.
Fourth quarter 2021 adjusted earnings per share was $0.14 per diluted share or 7.7% improvement over 2020.