UPC Ireland had 505,200 customers by the end of June, according to quarterly results from its parent company Liberty Global, down more than 3.5% on a year ago.
However the number of individual subscriptions at the cable network operator was up 0.7% to almost 1.1 million, meaning more of its customers were paying the company for multiple services.
UPC Ireland offers cable TV to customers, as well as broadband and phone services.
It is due to launch a mobile service later this year as part of a Mobile Virtual Network Operator agreement with Three.
The growth in UPC's subscription numbers compared to the second quarter of 2014 came from its broadband and phone services, which grew by 4.2% and 8.5% respectively.
Television subscriptions fell, however, down 8.5% in total with digital cable customers dropping by 5.3%.
Total quarterly revenue at Liberty Global - which has operations across Europe and the Americas - fell slightly year-on-year to $4.57 billion; $35.7m (0.8%) lower than in June 2015.
However the group said its rebased revenue, which takes into account the addition of Britain's Virgin Media to the figures, was up 3.3% year-on-year.