The Swiss group said staffing had been slower than usual in September, when traditionally companies take on workers after the summer months, particularly in top economies Germany and France.
The news sent Adecco shares tumbling 3.69 percent to €3.95 on the Swiss exchange.
It will also add to concerns about the health of Europe's stalling economy, after a key survey on Tuesday showed business activity in the 18-nation eurozone slowed this month.
Hiring is often seen as an important indicator for the health of an economy, with employers taking on temporary staff at the beginning of a recovery.
Adecco said revenue rose five percent in July and August, adjusted for currency fluctuations and trading days, in line with targets.