BACKGROUND Colchicine is effective for the treatment of acute pericarditis and first recurrences. However, conclusive data are lacking for the efficacy and safety of colchicine for treatment of multiple recurrences of pericarditis. METHODS We did this multicentre, double-blind trial at four general hospitals in northern Italy. Adult patients with multiple recurrences of pericarditis (≥two) were randomly assigned (1:1) to placebo or colchicine (0·5 mg twice daily for 6 months for patients weighing more than 70 kg or 0·5 mg once daily for patients weighing 70 kg or less) in addition to conventional anti-inflammatory treatment with aspirin, ibuprofen, or indometacin. Permuted block randomisation (size four) was done with a central computer-based automated sequence. Patients and all investigators were masked to treatment allocation. The primary outcome was recurrent pericarditis in the intention-to-treat population. This trial is registered with ClinicalTrials.gov, number NCT00235079. FINDINGS 240 patients were enrolled and 120 were assigned to each group. The proportion of patients who had recurrent pericarditis was 26 (21·6%) of 120 in the colchicine group and 51 (42·5%) of 120 in the placebo group (relative risk 0·49; 95% CI 0·24-0·65; p=0·0009; number needed to treat 5). Adverse effects and discontinuation of study drug occurred in much the same proportions in each group. The most common adverse events were gastrointestinal intolerance (nine patients in the colchicine group vs nine in the placebo group) and hepatotoxicity (three vs one). No serious adverse events were reported. INTERPRETATION Colchicine added to conventional anti-inflammatory treatment significantly reduced the rate of subsequent recurrences of pericarditis in patients with multiple recurrences. Taken together with results from other randomised controlled trials, these findings suggest that colchicine should be probably regarded as a first-line treatment for either acute or recurrent pericarditis in the absence of contraindications or specific indications. FUNDING Azienda Sanitaria 3 of Torino (now ASLTO2).