Swallowed coins are a frequent problem in paediatric practice. The majority that reach the stomach will pass unimpeded through the gastrointestinal tract. Prolonged gastric retention of a swallowed penny is reported in three children who had previously undergone pyloromyotomy for infantile hypertrophic pyloric stenosis. The coins were removed after laparotomy in two patients and endoscopically in the third. This abnormal retention may reflect a long-term disturbance of pyloric function after pyloromyotomy.