The prevalence of hereditary haemochromatosis (HH) was studied in Stockholm and Göteborg, the two largest cities in Sweden, using screening with transferrin saturation in combination with serum ferritin and further clinical and laboratory examinations. In Göteborg, none of 1660 men aged 50 and 51 years, randomly selected from the census register, was found to have HH. In Stockholm, nine out of 11,920 male hospital inpatients were diagnosed as having HH. The calculated mean and 95% confidence ranges were consistent with earlier findings in two studies on men in Malmö, the third largest urban area in Sweden. Pooling results from these three main urban areas, the mean prevalence was 0.073% (17/23, 355), which is considerably lower than figures reported from one area in northern Sweden and from pedigree analyses in several other areas in the world. Screening of the US population in the N-HANES II study also showed much lower figures. The reasons for these discrepancies are discussed and it is suggested that the average prevalence of HH in Caucasian populations is probably around 0.1%.