In the first nine months of 2009, revenues were £6.3bn, up 24.5% year on year. This partly reflected its acquisition of research outfit TNS and the weakness of the pound sterling against the US dollar and Euro.
However, on a like-for-like basis, excluding the impact of acquisitions and currency fluctuations, revenue was down 8.4%.
Its operations in Asia-Pacific, Latin America, Africa and the Middle East and Central and Eastern Europe, were least-affected by the economic downturn, WPP said.
But it noted western continental Europe "continues to be the worst affected region", followed by the US and UK.
Revenues from its media investment management operations, such as its media agencies MediaCom, Mindshare and MEC, were down 8.5% year on year. Public relations and public affairs revenues were down 8.3% year on year.
In a statement, Sorrell said: "There is little doubt that consumer and corporate confidence has recovered somewhat from the panic levels of the fourth quarter of 2008 and first quarter of 2009.
"Confidence, however, remains fragile among consumers, because of the shadow of high unemployment levels and among corporates, because Armageddon and Apocalypse now were barely avoided in September 2008."
He warned that, despite rising confidence, this "is still not transferring to their cheque-writing hands".