Fetal renal pelvic dilatation (pyelectasis) is readily identified at the routine second trimester anomaly scan. It is now well recognised that mild pyelectasis is associated with fetal chromosomal abnormalities and may predict neonatal renal anomalies. The reported prevalence of pyelectasis and the strength of the association with both aneuploidy and paediatric outcome varies considerably in the literature, making accurate prenatal counselling very difficult.