BACKGROUND: The study objective was to estimate temporal trends in ectopic pregnancy in a well-defined population. METHODS: We identified patients with ectopic pregnancy in hospital discharge registries in Sør-Trøndelag County, Norway, 1970-2004, and retrieved data from medical records. We calculated age-specific ectopic pregnancy incidence, proportions of patients with first ectopic pregnancy/prior infertility treatment, incidence of ectopic pregnancy by birth cohort and age and ratio of ectopic pregnancy to live births (extrauterine ratio) by age and parity. RESULTS: Age-adjusted ectopic pregnancy incidence rates increased from 4.3 to 16.0 per 10 000 women-years over the period 1970-1974 to 1990-1994 and declined to 8.4 per 10 000 women-years in 2000-2004. Incidences were highest among women aged 25-34 years throughout the study period. We observed decreases in proportions of women with previous ectopic pregnancy and with prior infertility treatment after 1990-1994. Incidence rates were the highest for women born between 1960 and 1964 in all age groups. Extrauterine ratio increased with age and was higher for women with two or more previous births compared with women with none or one prior birth. CONCLUSIONS: The epidemic increase in ectopic pregnancy towards 1990-1994 was followed by a marked decrease.