In the ongoing Zurich Cohort Study, 591 males and females from the general population of Zurich were interviewed five times over the 15-year period between the ages of 20 and 35 years. The data on sexual problems were mainly obtained from the final three interviews when the subjects were aged 28-35 years. Emotional problems or sexual dysfunction alone are rare and are almost always associated with each other, or with changes in libido. However, changes in libido without associated emotional problems or sexual dysfunction are relatively common. Libido therefore appears to be the core problem with which other sexual problems overlap. Overall, sexual problems of some type were found in 26% of normal subjects, 45% of non-treated depressed patients and 63% of treated depressed patients. This increase in sexual problems in treated depressed patients is mainly due to an increase in sexual dysfunction and emotional problems; the level of libido appears not to be affected by treatment. There was no difference in the prevalence of sexual problems of any kind between patients treated with medication and those treated only with psychotherapy.