The introduction of routine prenatal screening in the early 1980s resulted in paediatric urologists being confronted with the dilemma of what to do with antenatally-detected urinary tract dilatation, many of whom, we now know, do not require long-term surveillance or intervention. Similarly, the increasing use of abdominal imaging has resulted in a new challenge – what to do with asymptomatic renal cysts detected on ultrasound. Surgery is reserved for those that are symptomatic, compressive or have features of malignancy. There are few publications on the evolution and long-term outcomes of such cysts. Investigators from Indiana have previously shown that the modified Bosniak classification system is useful and that the vast majority of solitary renal cysts in children are simple; if asymptomatic, they require no other imaging evaluation. Here, O’Kelly et al. (Children’s Hospital of Eastern Ontario) have reviewed the outcomes of 783 children found to have renal cysts on abdominal ultrasound imaging. Of these, 211 had complex cysts and only four (1.8%) had renal cancer detected at surgery. There was a small (<1%) incidence of conversion from simple to complex cyst on ultrasound in older teenagers with a larger cyst (>15mm) at presentation. Complete regression was seen in a quarter of renal cysts overall. The authors conclude that most asymptomatic renal cysts are benign, and if simple and <15mm, the patient could be scanned again in two years and discharged assuming stability is demonstrated. Larger simple cysts (>1.5cm), complex cysts, patients with a family history of adult polycystic kidney disease or those with other genitourinary anomalies requiring ongoing follow-up should be serially followed.