Abstract Background The development of laparoscopy as a means of evaluation and treatment of inguinal hernia in children has raised the question of whether simultaneous closure of a contralateral patent processus vaginalis (CPPV) is justified. The present study aimed to determine the rate of metachronous inguinal hernia (MIH) in children with CPPV. Methods Children with unilateral inguinal hernia from two hospitals underwent either open or laparoscopic repair, and were followed up for MIH. The presence of CPPV was evaluated during laparoscopy and, if detected, the CPPV was closed. The relationship between CPPV and subsequent MIH was studied. Results The study included children who had complete follow-up (90·0 per cent of those having open repair and 92·2 per cent of those undergoing laparoscopic repair). Of 2538 children who had open hernia repair, 62 (2·4 per cent) developed MIH (30 on the right side and 32 on the left; P = 0·015). Among 2855 children who underwent laparoscopic repair, a CPPV was identified and closed in 1469 (51·5 per cent). The rate of MIH after negative laparoscopic evaluation for CPPV was three of 2855 (0·1 per cent). There were no significant differences in the rate of CPPV between sexes and either the right or left side (P = 0·072 and P = 0·099 respectively). Ipsilateral recurrence was less frequent after laparoscopic repair: seven (0·2 per cent) versus 26 (1·0 per cent) for open repair (P < 0·001). Conclusion Laparoscopic inguinal hernia repair was associated with a lower recurrence rate than open repair. Routine repair of CPPV reduced the rate of subsequent MIH, but 21 CPPVs needed to be closed to prevent one MIH.