BACKGROUND: Reports on increasing hypospadias trends are based on birth defect registries, which are prone to inaccuracy. We assessed the prevalence of hypospadias precisely, by prospective examination of all newborns in Rotterdam over a 2-year period. METHODS: A total of 7292 consecutive male births were examined for the presence of hypospadias, classified by severity. RESULTS: The frequency of hypospadias in newborn boys was 0.73% (53/7292). The rate among live births was 38 per 10 000, which is 6 times the previously reported rate for the Southwestern Netherlands (6.2) ( P < 0.0001). This registry excludes glandular hypospadias. Without glandular cases, our rate is 26 per 10 000, which is still 4-fold higher ( P < 0.0001). The ratio of minor to major hypospadias was 0.3. In 79% of cases, surgery was indicated. CONCLUSIONS: We found a 4-fold higher than expected hypospadias rate, which may be explained by case ascertainment differences. The proportion of major cases was higher than generally assumed. This study provides evidence for substantial geographical differences. Explanations for temporal and geographical differences need to be explored. To monitor hypospadias rates and trends accurately, complete case ascertainment, including standardized classification of severity, is warranted.