Background: Cloacal anomalies are rare abnormalities with highly variable forms, which makes them difficult to diagnose antenatally. We present a cloacal anomaly case with interesting antenatal ultrasonographic findings. Case: A 24-year-old woman, gravida 1, para 0, presented at 23 weeks’ gestation with ultrasonographic evidence of fetal ascites. Between 23 and 30 weeks’ gestation, serial ultrasounds showed changing features of a cloacal anomaly, consisting of fetal ascites, a cystic pelvic mass, hydronephrosis, and oligohydramnios. Conclusion: Serial antenatal ultrasound helped diagnose changing features of a cloacal anomaly in our case, thus allowing directed antenatal counseling and appropriate perinatal treatment.