Incidence of prostate cancer has increased steadily in Norway since the cancer registration started in the 1950s. In Oslo, however, the figures show decreasing incidence since the 1970s, a trend not observed in any other region. These changes have occurred in the groups older than 70 years of age. The most important change is a marked decrease in the number of cases first diagnosed at autopsy, from 12.7% in 1957-61 to 3.8% in 1987-91. However, even after these cases are excluded, a slight downward trend in incidence still exists. The same tendencies are not observed for other forms of cancer. It seems as if the diagnostic intensity has become lower in Oslo than in the rest of the country. This pattern may be explained by a change of priority in diagnostics, owing to scarce resources, but other reasons, such as stabilization of the incidence of prostatic cancer, are also possible.