The Dutch company, which trails its Swiss rival Adecco, said its "gross margin is expected to be modestly lower sequentially" in the first quarter.
In the last three months of 2018, sales dropped in major European economies such as France, Germany and Italy. In the United States, where Randstad operates the Monster jobs site, sales rose 3 percent.
Fourth-quarter underlying earnings came in at 309 million euros (£270.9 million), compared with 305 million euros a year earlier. Analysts polled by the company had expected earnings before interest, taxation and amortisation (EBITA) of 305 million euros.
Sales of 6.1 billion euros in the three months ended Dec. 31, 2018 were in line with forecasts, while net income slipped 2 percent to 194 million euros.
(Reporting by Anthony Deutsch; Editing by Subhranshu Sahu and Sherry Jacob-Phillips)