The aim of this retrospective study was to evaluate the impact of resident participation in the results of surgical treatment in 1149 consecutive patients operated for biliary disease between January, 1980 and December, 1987 at the Instituto Nacional de la Nutrición "Salvador Zubirán". Patients were divided in three groups: GROUP I. 640 cases treated by surgical residents under a senior surgeon supervision. GROUP II. 168 patients operated by the chief surgical resident. GROUP III. 341 patients treated by senior staff surgeons. Age, sex and risk factors were similar between groups. Residents performed more operative cholangiograms (p less than 0.05). In general, senior surgeons performed more transduodenal sphincteroplasties (p less than 0.05) and other additional procedures like appendectomies and gastrostomies during the same surgery. Wound infection was more frequent in group III patients (p less than 0.005) but there was no significant clinical difference in other postoperative complications like intraabdominal abscess, bile fistula, wound dehiscence, intraabdominal bleeding, iatrogenic injury of the biliary tract, and residual common duct stone. The duration of the in-hospital convalescence period was similar in all three groups. The mortality rate for the total series was 2.2%. In group II there were more patients affected for acute cholecystitis, and more patients died postoperatively (p = less than 0.01). We may consider this difference attributable to the more complex patients handled by the chief resident. Mortality rate among patients with chronic biliary tract disease was less than 1%. We were not able to demonstrate any significant difference in mortality and complication rates between those patients operated by residents, chief residents and senior surgeons.(ABSTRACT TRUNCATED AT 250 WORDS)