The 5,000 job cuts will be split equally over the next two years, and will be in addition to the 2,300 redundancies already announced earlier this year.
Stephen Carter, NTL managing director, said, "If all else remains the same, my view is that this business should be run on a headcount of 15,000."
The company employs 19,500 staff, who are based mostly in the UK.
The news came as NTL announced second-quarter results with revenues up at £634m from £434m last time. Ebitda rose 26% on last time to £115m.
The group's shares rose to $8.51 (£5.96) in early trading in New York after hitting a low of $4.75 (£3.32) last week.
The company also said it had appointed advisers to look into how it could release some capital from its $2.5bn broadcast business.
A partial flotation of the business, which brought in £59m in revenues during the second quarter, has been mooted for some time until it emerged in June that NTL was considering other possibilities.
The money raised from the sale would help allay investors' fears about the group's burgeoning £12bn mountain of debt.
The cable operator said it was on track to reach its target of 1.25m digital TV subscribers and 100,000 cable modem customers by the year-end.
NTL increased subscriptions to its digital TV service by 26%, bringing the total to 951,300, while cable modem customer numbers climbed 74% to 45,750.