Schoolteachers, nurses and doctors in primary health care in Stovner district, Oslo, have developed a new programme of sexual education for teenagers 14-16 years of age. The aim of the programme is to increase the knowledge about sexually transmitted diseases, reproduction and prevention of pregnancy and to open up for discussions within the classes about love, ethics, sexual abuse and sexual pressure. To evaluate the programme, pupils in the 9th grade in 1991 and 1993 (about 16 years old) answered a self-administered questionnaire. The answers showed an increase in knowledge about sexually transmitted diseases and reproduction, and a reduction in the percent of pupils who had sexual intercourse. The result should be cautiously interpreted, since changes in sexual knowledge and practices over time may have been caused by factors other than the intervention.