Background: The aim of the study was to assess changes in sexual attitudes and sexual behaviour related to HIV/sexually transmissible infections (STI) during a long period of intensive efforts by the Swedish authorities to curb the spread of HIV. Methods: We conducted mailed questionnaire surveys in random samples of the Swedish general population in 1989, 1994, 1997, 2000, 2003 and 2007 (total n = 16773). Each sample consisted of some 4000–6000 participants aged 16–44 years, stratified by age: 16–17, 18–19, 20–24, 25–34 and 35–44 years. The overall participation rate was 61.6% (for men, 53.5%; for women, 69.9%). Results: Between 1989 and 1994, the proportion of participants holding a restrictive view on sexual intercourse outside a stable relationship decreased significantly. The surveys since 1994 do not show any change in that respect. The prevalence of several sexual partners increased significantly throughout the period of study. The prevalence of casual sexual intercourse without the use of a condom also increased significantly from 1989 until 2003, but decreased slightly between 2003 and 2007. This change in sexual behaviour was more prominent in women than among men. The prevalence of several sexual partners and casual sexual intercourse without the use of a condom was significantly higher for the younger than for the older age cohorts. Conclusions: The study demonstrates the need for a continuous preventive campaign against HIV/STI in the general population in Sweden, particularly among young people.