['Since 1995 we have, at our centre, adopted a selective approach to performing micturating cystourethrograms (MCUGs) on patients with antenatally diagnosed hydronephrosis. This study reviews the outcome of this policy.', "We carry out MCUGs only if any of the following features are present on ultrasound: bilateral hydronephrosis, ureteric dilatation, renal scarring, bladder wall thickness greater than 5mm, or presence of a duplex system or ureterocele. Patients with simple unilateral hydronephrosis are excluded, and are managed with 6 months' trimethoprim prophylaxis and ultrasound surveillance with a minimum of 3 years' follow up.", 'Fifty-five patients were referred with an antenatal diagnosis of hydronephrosis between 1999 and 2002; 26 (47%) did not have an MCUG. Of these, five had increasing hydronephrosis and required surgery for pelvi-ureteric junction obstruction, and three had a multicystic dysplastic kidney on postnatal scanning. In the remaining 18 patients, the hydronephrosis resolved spontaneously, with no renal scars or asymmetry. During follow up, none of these patients had a urinary tract infection.'] Are micturating cystourethrograms necessary for all cases of antenatally diagnosed hydronephrosis?