Background: Up to one-third of patients with an inguinal hernia have no symptoms from the hernia. The aim of this study was to determine the long-term outcome of patients with a painless inguinal hernia randomized to observation or operation. Methods: Some 160 men aged 55 years or more with a painless inguinal hernia were randomized to observation or operation between 2001 and 2003. All were invited to attend a research clinic at 6 and 12 months, and 5 years after randomization. Those unable to attend for clinical review were sent a questionnaire based on the clinical review pro forma. Results: After a median follow-up of 7·5 (range 6·2-8·2) years, 42 men had died (19 in the observation and 23 in the operation group); 46 of the 80 men randomized to observation had conversion to operation. The estimated conversion rate (using the Kaplan-Meier method) for the observation group was 16 (95 per cent confidence interval 9 to 26) per cent at 1 year, 54 (42 to 66) per cent 5 years and 72 (59 to 84) per cent at 7·5 years. The main reason for conversion was pain in 33 men, and two presented with an acute hernia. Sixteen men developed a new primary contralateral inguinal hernia and three had recurrent hernias. There have been 90 inguinal hernia repairs in the 80 patients randomized to surgery compared with 56 in those randomized to observation. Conclusion: Most patients with a painless inguinal hernia develop symptoms over time. Surgical repair is recommended for medically fit patients with a painless inguinal hernia.