One in four older couples never make love - but most still say they couldn't be happier.
Trust, kindness, friendship and a sense of humour were all seen as more important in a relationship than sex, a survey of over-50s found.
A third of respondents said they made love at least once a week, with 2 per cent being intimate every day. But almost a quarter of those in long-term relationships said they had no sex at all.
Of these, just under half said they missed it, but the majority - 57 per cent - claimed to be perfectly happy without it.
Cari Rosen, editor of the website Gransnet which carried out the survey, said: "While passion is undoubtedly important for most people, it turns out that the glue in successful long-term relationships is compassion, kindness, generosity and friendship - which is advice that people of any age can use."
She added: "Lots of younger people don't like to think about older people having loving relationships and good sex, which is odd when you consider that for many of us it's the best case scenario."
Gransnet is a social networking site for the over-50s, created as a spin-off from the popular Mumsnet. Users can chat and seek advice on a range of topics, from fashion and gardening to grandparenting and travel.
The survey, in partnership with relationship counselling service Relate, aimed to "give a true picture of sex and love in later years".
Its findings were based on responses from 634 Gransnet users aged 51 to 85, who were asked what made relationships last. Almost all - 98 per cent - said trust was important, followed by mutual support, kindness, communication and friendship.
Love was crucial for almost everyone, along with a sense of humour. Sex, however, was only regarded as important by two-thirds of those quizzed. More than half also said they thought younger adults 'don't like to think about older people having sex' and that they never discussed the topic with family and friends.
Those who had been in a relationship for more than a year - with the average couple together for 32 years - said their love-making had improved over time. Asked for their tips on keeping the passion alive in the bedroom, nearly three-quarters said having a good imagination was important.
When it came to discussing sexual problems with their GP, 37 per cent said they would be too embarrassed - but 47 per cent indicated they would ask for help.
The survey also found many single grandparents embraced internet dating, with 34 per cent of those who had found love after the age of 55 meeting their partner online.
Relate counsellor and sex therapist Clare Prendergast said: "It's great that many grandparents are having regular sex but it's also very possible to have a healthy, loving and intimate relationship without sex being on the agenda.
"As these survey results show, it's trust, kindness and mutual support which people often value most. But if you are missing sex and intimacy in your relationship, there are plenty of things you can do to get the spark back."
- Daily Mail