Patients with infantile hypertrophic pyloric stenosis (IHPS) have an increased incidence of renal anomalies. Association of IHPS and polycystic kidney disease (PKD) has been reported in three case histories. It is uncertain whether the association of PKD and IHPS is due to genetics, a pathophysiological link or a chance phenomenon. One hypothesis linking the two conditions is nitric oxide synthetase (NOS) deficiency. NOS deficiency leads to lack of locally available nitric oxide causing a failure of smooth muscle relaxation. It is therefore plausible that NOS deficiency plays a part in the pathogenesis of pyloric stenosis, hypertension and cyst development in autosomal-dominant PKD.