This prospective study determines the indications for and the optimal timing of laparoscopic cholecystectomy (LC) following the onset of acute cholecystitis. It also evaluates preoperative and operative factors associated with conversion from laparoscopic cholecystectomy to open cholecystectomy in the presence of acute cholecystitis. Having been established as the procedure of choice for elective cholelithiasis, LC is now also used for management of acute cholecystitis. Under these circumstances the procedure may be difficult and challenging. Certain favorable and unfavorable conditions may be present that influence the conversion and complication rates. Information about these conditions may be helpful for elucidating the optimal circumstances for LC or when the procedure is best avoided. We performed LC on an emergency basis as soon as the diagnosis was made on all patients presenting with acute cholecystitis from January 1994 to December 1995. All preoperative, operative, and postoperative data were collected on standardized forms. Of the 137 patients registered, 130 were eligible for the audit. Seven patients found by laparoscopic intraoperative cholangiography to have choledocholithiasis were converted for common bile duct exploration and were excluded from the study. Altogether 83 patients (72%) underwent successful LC and 37 (28%) needed conversion to open cholecystectomy. The conversion rate of acute gangrenous cholecystitis (49%) was significantly higher than that for uncomplicated acute cholecystitis (4.5%) (p < 0.00001) and for hydrops (28.5%) and empyema of the gallbladder (28.5%) (p = 0.004). The difference in conversion between the group with acute necrotizing (gangrenous) cholecystitis and the two groups with hydrops and empyema of the gallbladder was not statistically significant (p = 0.07). The complication rates of acute cholecystitis, hydrops, empyema of the gallbladder, and gangrenous cholecystitis were 9.0%, 9.5%, 14.0%, and 20.0%, respectively (p = NS). Patients with an operative delay of 96 hours or less from the onset of acute cholecystitis had a conversion rate of 23%, whereas a delay of more than 96 hours was associated with a conversion rate of 47% (p = 0.022). The complication rate was 8.5% in the laparoscopic group and 27% in the converted group (p = 0.013). Patients over 65 years of age, with a history of biliary disease, a nonpalpable gallbladder, WBC count over 13,000/cc, and acute gangrenous cholecystitis were independently associated with a high LC conversion rate; male patients, finding large bile stones, serum bilirubin over 0.8 mg/dl, and WBC count over 13,000/cc were independently associated with a high complication rate following laparoscopic surgery with or without conversion. Generally, LC can be performed safely for acute cholecystitis, with acceptably low conversion and complication rates. Different forms of cholecystitis carry various conversion and complication rates in selected cases. LC for acute cholecystitis should be performed within 96 hours of the onset of disease. Predictors of conversion and complications may be helpful when planning the laparoscopic approach to acute cholecystitis.