Some 70% of South African men experience some sort of sexual dysfunction, according to data debated at a conference on sex in Africa.
By Ania Lichtarowicz
BBC health correspondent, Johannesburg
The figures are considerably higher than in developed countries.
Doctors at the conference are concerned that these sexual problems are having a wide effect on people's well-being.
Erectile dysfunction covers many sexual problems - including not being able to have an erection, premature ejaculation and not achieving orgasms.
Importance of sex
This study, carried out in the Western Cape, addresses types of problems about which there is very little data from Africa.
In the US the figures of the same age group are around 30%.
Why there is such a difference is unclear.
This type of problem has much wider implications though - causing relationship problems, depression and can lead to violence.
A recent survey in South Africa showed that some men consider sex more important than food or shelter, which is why the topic is so high on the agenda at first African Congress on Sexual Health and Rights.
Many new treatments are being developed for erectile dysfunction.
Yet despite their high cost doctors in Africa say that people are willing to spend what little money they have on their sexual enjoyment.