The incidence of prostate cancer has increased markedly during the past half century. We used the data from the Swedish Cancer Registry to follow the incidence trends and age-specific incidence up to 2002. Two different patterns in the age-incidence relationships were noted. The first one, prevailing until about 1995, was characterized by a preferential increase in incidence in men older than 70 years. In the second pattern, the increase extended preferentially to younger age groups, and it coincided with an introduction of opportunistic prostate specific antigen (PSA) screening, which was the probable cause of the large upward shift in the incidence between 1998 and 2000. The possible effects of diagnostic methods on familial risk estimates were tested by comparing age and calendar time differences among brothers who were diagnosed with prostate cancer, retrieved from the Swedish Family-Cancer Database. The 2 distributions were very different according to the Wilcoxon rank test (p < 0.0001). The data suggest that a diagnosis of prostate cancer in 1 brother leads to an early diagnosis in a second brother. The data are probably explained by the healthy brother seeking medical advice upon diagnosis in another brother. This effect is likely to bias familial risk estimates.