Trips to Ireland from the UK decreased by almost 6pc in the three months to March, according to the latest data released by the Central Statistics Office (CSO).
The drop-off will be of concern to the Irish tourist industry, which depends on UK visitors for a large proportion of its revenue.
While Irish tourism posted record growth in 2016, policy makers will be hoping the latest data is not a harbinger of what is to come once Brexit kicks in. UK visitors still represent the largest proportion of tourists to Ireland with 789,200 trips made between December and the end of February.
That represents a fall of 5.9pc compared to the same period last year, or almost 50,000 fewer people.
Tourism Ireland told the Irish Independent the figures reflect a trend that is being reported by hoteliers and visitor attractions across the country in recent months. The drop in sterling and increased general uncertainty arising from Brexit have been flagged as the major reasons for the fall off in numbers.
Niall Gibbons, CEO of Tourism Ireland, said: "Economic uncertainty is making British travellers more cautious about their discretionary spending, which is impacting on travel to Ireland."
Overall, tourists levels over the three months were up by 3pc. Visits from other EU countries rose 0.7pc. There was a spike in visits from North America, up 38.2pc compared with a year earlier.