BACKGROUND Cloacal exstrophy (CE) is the most severe manifestation of the epispadias-exstrophy spectrum. Previous studies have indicated an increased rate of renal anomalies in children with classic bladder exstrophy (CBE). Given the increased severity of the CE defect, it was hypothesized that there would be an even greater incidence among these children. OBJECTIVE The primary objective was to characterize renal anatomy in CE patients. Two secondary objectives were to compare these renal anatomic findings in male and female patients, and female patients with and without Müllerian anomalies. METHODS An Institutional Review Board-approved retrospective review of 75 patients from an institutional exstrophy database. Data points included: age at analysis, sex, and renal and Müllerian anatomy. Abnormal renal anatomy was defined as a solitary kidney, malrotation, renal ectopia, congenital cysts, duplication, and/or proven obstruction. Abnormal Müllerian anatomy was defined as uterine or vaginal duplication, obstruction, and/or absence. RESULTS The Summary Table presents demographic data and renal anomalies. Males were more likely to have renal anomalies. Müllerian anomalies were present in 65.7% of female patients. Girls with abnormal Müllerian anatomy were 10 times more likely to have renal anomalies than those with normal Müllerian anatomy (95% CI 1.1-91.4, P = 0.027). CONCLUSIONS Patients with CE had a much higher rate of renal anomalies than that reported for CBE. Males and females with Müllerian anomalies were at greater risk than females with normal uterine structures. Mesonephric and Müllerian duct interaction is required for uterine structures to develop normally. It has been proposed that women with both Müllerian and renal anomalies be classified separately from other uterine malformations on an embryonic basis. In these patients, an absent or dysfunctional mesonephric duct has been implicated as potentially causal. This provided an embryonic explanation for uterine anomalies in female CE patients. There were also clinical implications. Women with renal agenesis and uterine anomalies were more likely to have endometriosis than those with isolated uterine anomalies, but were also more likely to have successful pregnancies. Males may have had an analogous condition with renal agenesis and seminal vesicle cysts. Future research into long-term kidney function in this population, uterine function, and possible male sexual duct malformation is warranted. CONCLUSIONS Congenital renal anomalies occurred frequently in children with CE. They were more common in boys than in girls. Girls with abnormal Müllerian anatomy were more likely to have anomalous renal development. Mesonephric duct dysfunction may be embyologically responsible for both renal and Müllerian maldevelopment.