MDC Partners, home to Kwittken & Company, Allison & Partners, Lime PR, and other firms, reported a 33.4 percent increase in revenue for Q3; from $178.6 million in 2010 to $238.2 million for the same period in 2011.

Organic growth also took a leap, up 17.9 percent for the quarter.

However, in a statement, MDC CEO Miles Nadal said the company’s EBITDA guidance had shifted downward because of a “slowing of existing client work as well as some modest delays in new projects and campaigns.” (Here’s a definition of EBITDA.)

EBITDA for the quarter decreased 21.1 percent from $20.6 million in Q3 2010 to $16.3 million in Q3 2011. EBITDA for the year is expected to be $90 million to $100 million.

“Despite this revision, we remain in an enviable position and are on track to post year-over-year revenue and EBITDA growth for the full-year 2011,” continued Nadal’s statement. He expressed optimism for organic revenue in 2012.

Revenue for the first nine months of 2011 were $696.2 million, up 43.7 percent from 2010, which have revenue totaling $484.4 million. Organic revenue is up 21.5 percent for the period.

For more info about MDC’s earnings, click here.