OBJECTIVE: In patients who have undergone a potentially curative resection of colorectal cancer, does a 'second-look' operation to resect recurrence, prompted by monthly monitoring of carcinoembryonic antigen, confer a survival benefit? DESIGN: A randomised controlled trial recruiting patients from 1982 to 1993 was recovered under the Restoring Invisible and Abandoned Trials (RIAT) initiative. SETTING: 58 hospitals in the UK. PARTICIPANTS: From 1982 to 1993, 1447 patients were enrolled. Of these 216 met the criteria for carcinoembryonic antigen (CEA) elevation and were randomised to 'Aggressive' or 'Conventional' arms. INTERVENTIONS: 'Second-look' surgery with intention to remove any recurrence discovered. PRIMARY OUTCOME MEASURE: Survival. RESULTS: By February 1993, 91/108 patients had died in the 'Aggressive arm' and 88/108 in the 'Conventional' arm (relative risk=1.16, 95% CI 0.87 to 1.37). By 2011 a further 25 randomised patients had died. Kaplan-Meier analysis showed no difference in long-term survival. CONCLUSIONS: The trial was closed in 1993 following a recommendation from the Data Monitoring Committee that it was highly unlikely that any survival advantage would be demonstrated for CEA prompted second-look surgery. This conclusion was confirmed by repeat analysis of survival times after 20 years. TRIAL REGISTRATION NUMBER: ISRCTN76694943.