UPC has lost 36,000 television subscribers in Ireland, as its TV business fell by 9pc in the last 12 months.
The company blames "increased competition" for its "under-performance".
In its latest set of company accounts, UPC said its overall Irish TV subscriber base fell from 422,700 to 386,500 over the last year.
It also said that its overall Irish customer base fell from 530,600 to 511,800 over the same period.
However, its Irish broadband business grew by 17,500, or 5pc, from 348,300 to 365,800 subscriptions in the last 12 months. Its telephone business also grew by 36,600.
UPC's biggest television rival, Sky, is understood to have over 700,000 television customers in the Irish market. The satellite operator has added over 30,000 broadband subscribers in the last year and now has just under 100,000 internet customers here.
UPC declined to give specific financial details about its Irish business. However, the operator's overall revenue for Ireland and the UK fell by 7.4pc (€121m) from €1.65bn to €1.52bn over the last 12 months.
Operating cash flow for the two countries combined fell by 3.6pc (€25.2m) from €706m to €680m. However, the operator's average revenue per user across Ireland and the UK rose by 1.2pc to €66.86 per month.
UPC also said that its acquisition of the Irish wifi operator Bitbuzz, completed in December 2014, added 8pc to its first quarter 2015 revenues, although it declined to give further details on figures.
"Under-performance in Germany, the Netherlands and Ireland drove the majority" of negative impact on the company's European business, according to the accounts.
UPC is set to launch a new Irish mobile operator service in the second half of this year.
The service is expected to combine with the operator's broadband, television and home telephone services to form a 'quad play' package.
UPC could face new competition in the broadband market over the next 12 months with new fibre services from Vodafone and Eircom set to launch in some parts of the country.
"UPC has had a positive start to the year and is continually making strong progress," said Carol Grennan, UPC's chief financial officer.
"We are seeing solid results from the recent acquisition of Bitbuzz."