ABSTRACT. Objective. Maternal risk factors for hypospadias are poorly defined, and there is debate about temporal trends in hypospadias prevalence. We examined select maternal characteristics as possible risk factors for hypospadias among male offspring and evaluated yearly prevalence rates in Washington State.Methods. We performed a population-based, casecontrol study using linked birth-hospital discharge data from Washington State for 1987-1997 and prevalence data for 1987-2002. All cases of hypospadias were identified on the basis of International Classification of Diseases, Ninth Revision, codes from the birth hospitalization (N ؍ 2155). Five control subjects were randomly selected for each case subject from the remaining singleton births, frequency matched according to year of birth (N ؍ 10 775). Maternal and infant characteristics were ascertained from the birth certificate. Logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs). Yearly prevalence was determined by dividing the total number of hypospadias cases by the number of male singleton live births for each year.Results. The risk of delivering an affected male infant increased with advancing maternal age; relative to women <20 years of age, those >40 years of age were at greatest risk (OR: 1.70; 95% CI: 1.17-2.48). Infants of nonwhite women were generally at decreased risk. Infants born to women with preexisting diabetes mellitus were at greater risk than those born to women without diabetes (OR: 2.18; 95% CI: 1.03-4.60); however, this was not observed for infants born to women with gestational diabetes. The birth prevalence of hypospadias in 2002 was 5.0 cases per 1000 male births, not significantly different from that in 1987.Conclusion. Older maternal age, white race, and preexisting diabetes were associated with increased risk of hypospadias among male offspring. H ypospadias is one of the most common congenital anomalies in the United States, with an estimated prevalence of 3 to 8 cases per 1000 male births. 1,2 The malformation is the result of incomplete fusion of the urethral folds, which usually occurs between 9 and 12 weeks of gestation. Although the success rate for surgical repair is high, 3 the high prevalence of hypospadias translates into a significant financial burden on the health care system. When rare complications do occur, the resultant morbidity of corrective procedures, psychologic stress, and potential loss of function can be devastating to the patient and family.Although hypospadias is common, risk factors for this birth defect are relatively poorly defined. Familial aggregation is well recognized. 4 It has been established that low birth weight and shorter gestation are associated with hypospadias, 5-7 but other risk factors are more controversial. At least 2 studies have suggested that older maternal age may be a risk factor for hypospadias, 1,8 but both of those studies relied on data from the same birth defects registry. Studies that examined race as a potential risk factor have...