The company said that revenue growth in the first four months of this year was "satisfactory", and that it had attracted new business worth $850m (£597m) during the period.
The Carat network, which has clients including Vodafone and Pfizer, gained new business of $2bn (£1.4bn) in 2000.
However, its share price dropped by 9.89% to 123p in afternoon trading on Wednesday, in response to the warning of a slowdown in spending by several clients.
In a statement, the company said: "This is particularly marked in the US, where there has been a widely reported slowdown in the economy, most noticeably in the high tech sector. Europe continues to trade well, albeit at slightly lower growth rates than seen earlier in the year."
In a separate announcement, Aegis said that its market research network, Aegis Research, had acquired MEMRB Custom Research Worldwide, which has offices in 22 countries throughout central, eastern and southern Europe, the Middle East and North Africa, and associate offices in another eight countries
It also bought Demoscopie, a French market research firm. It did not reveal the terms of either deal.
www.aegisplc.com