Recurrence is a major problem in the medical treatment of gallstones but its extent is still uncertain. The aim of this study was to determine the magnitude of this event and to assess the effectiveness of a postdissolution treatment in preventing it. We evaluated the long-term recurrence rate after 96 confirmed dissolutions observed in 86 subjects (71 women, 15 men) over a 12-yr follow-up period. A low-dose postdissolution treatment (ursodeoxycholic acid, 300 mg/day) was administered to 36 subjects, whereas in the remaining 60 cases no postdissolution treatment was given. By actuarial life-table analysis, the cumulative proportion of gallstone recurrence was 12.5% at the first year, rising to 61% at the 11th year. Postdissolution treatment was effective in reducing the frequency of gallstone recurrence (p = 0.0067), but this was mainly related to its effect on younger subjects (less than or equal to 50 yr old). In older subjects the recurrence rate was unaffected by treatment. The probability of gallstone recurrence was significantly higher in subjects with multiple stones before dissolution treatment than in those who had had solitary stones (p = 0.0091). No other factor predictive of gallstone recurrence could be identified.