The country's services sector expanded strongly in December to mark three and a half years of unbroken growth, as the economy outpaced its European peers in 2015 for a second successive year.
The Investec Purchasing Managers' Index of activity in services, which covers businesses from banks to hotels, slipped to 61.8 from November's nine year high of 63.6.
But the index remains well above the 50 mark that denotes growth in activity. It last fell below 60 in February 2014 when Ireland was emerging from a three-year international bailout.
Investec said that the employment sub-index, which reached a record high of 62.0 in November, dropped to an eight-month low of 58.6 last month.
But it noted that increasing backlogs of work should support ongoing growth in employment in the sector throughout 2016.
"Within the survey we see evidence that improving conditions, both at home and abroad, are supporting growth in new business," Investec Ireland chief economist Philip O'Sullivan said.
"With the expectations component continuing to stand well above the series average, Irish services firms remain bullish about their future prospects. Given the positive outlook for Ireland's key trading partners and the domestic resurgence, we share this confidence," he added.