The rate of overdiagnosis of prostate carcinoma was assessed by following 6890 participants in pilot screening studies from 1991 to 1994. Observed/expected incidence and mortality were determined using data from the Cancer and Mortality Registry. The cancer detection rate (1.75%) and observed/expected ratio (12.5:1) were high at the first screening, and substantially lower at the second screening (0.65% or 4.10:1). According to the registry follow-up, prostate cancer occurred in 225 subjects in the whole study cohort, while 178.2 were expected with 50652 men/years at risk. The standardised incidence rate was 1.66 in the screened (95%CI=1.4-2.0), 0.97 in the non-responders (95%CI=0.8-1.2) and 1.23 in subjects excluded from invitation due to previous cancer or major illness (95%CI=0.8-1.5). A 66% excess incidence rate was observed in the screened subjects over a 9-year period, confirming previous estimates of overdiagnosis.