A study was carried out to quantify and describe patients seen in sexually transmitted diseases clinics in England and Wales during 1978. Nine per cent of male patients were homosexual and 58% of female patients were under 25 years compared with only 42% of heterosexual men. Homosexual men had a higher mean number of cases per patient during the year than heterosexual men or women, largely because thay were more likely to have multiple episodes of disease. Female patients also had a higher mean number of cases than heterosexual men, because they often had several concurrent infections. There were 100,000 fewer patients than cases (322,000 compared with 432,000); 41% were seen in clinics in London. These findings show that current statistics for STDs are inadequate. Some quantification and categorisation of patients treated would be useful in analysing the trends in the incidences of the STDs.