Background: Male genital anomalies often require surgery in early life to address functional and cosmetic consequences. However, there has been little assessment of developmental outcomes of affected boys. Methods: We conducted a population-based cohort study of all boys born in New South Wales, Australia, and undergoing school-entry developmental assessment in 2009 or 2012. Health and developmental information was obtained by means of record-linkage of birth, hospital and Australian Early Development Census data. Boys with hypospadias or undescended testis (UDT) were compared with those without. Developmental outcomes were assessed in five domains (physical health, emotional maturity, communication, cognitive skills, and social competence), and boys were categorized as vulnerable (<10(th) centile of national scores), developmentally high risk (DHR; vulnerable in 2+ domains), and special needs. Results: We included 420 boys with hypospadias, 873 with UDT, and 77,176 unaffected boys. There was no difference in the proportion of boys developmentally vulnerable in any domain or DHR between boys with hypospadias (DHR: n = 49; 13.1%; p = 0.9), UDT (n = 116; 15.2%; p = 0.06), and unaffected boys (n = 9278; 12.9%). Compared with unaffected boys (n = 4826; 6.3%), boys with hypospadias (n = 43; 10.2%; p <0.001) or UDT (n = 105; 12.0%; p <0.001) were more likely to have special needs. Stratified analyses revealed that only boys with UDT and coexisting anomalies had increased risk of being DHR (odds ratio: 2.65; 95% confidence interval, 1.61-4.36) or special needs (odds ratio: 2.91; 95% confidence interval, 2.00-4.22). Conclusion: We found no increased risk of poor development among boys with hypospadias or UDT. However, boys with UDT and coexisting anomalies were more likely to have poorer development and special needs. (C) 2017 Wiley Periodicals, Inc.