In a 20-year longitudinal study on ectopic pregnancy in a defined population of women aged 15-39 years the rate of ectopic pregnancy per 1000 diagnosed conceptions increased from 5.8 during 1960-4 to 11.1 during 1975-9. The mean annual incidence of ectopic pregnancy per 1000 women increased from 0.6 to 1.2 during the same period. The numbers of ectopic pregnancies per 1000 diagnosed conceptions increased with increasing age of the women and were 4.1, in the teenage group 6.9, in women aged 20-29 years, and 12.9 in women aged 30-39. Among 20- to 29-year-old sexually active women at risk of pregnancy who had never had acute salpingitis the rates of ectopic pregnancy per 100 woman-years were the same in those who did not use contraceptives as in those using non-medicated or copper-medicated intrauterine contraceptive devices (IUCDs; 0.3/100 woman years). The risk of an ectopic pregnancy increased sevenfold after acute salpingitis. These findings confirm the increased risk of ectopic pregnancy after salpingitis and suggest that the increase in the incidence of ectopic pregnancy in Lund from 1960 to 1979 was partly accounted for by the use of IUCDs.