We investigated the incidence of unsuspected gallbladder (GB) carcinomas in a total of 527 consecutive GB specimens resected for benign biliary disease and their clinicopathological features. The GBs were examined microscopically using stepwise tissue sections at 5 mm interval. Clinical and pathological findings were analysed in the cases of unsuspected carcinoma. The 527 patients included 314 women and 213 men (mean age 56.1 years). The incidence of unsuspected GB carcinomas detected during or after cholecystectomy was 1.89%. In ten patients with unsuspected carcinomas, symptoms and signs were nonspecific. Abdominal US showed GB stones (8), thickening of GB wall (1), empyema (2) and a polyp (1). Macroscopically, infiltrative type was the most common. Microscopic examination showed tubular adenocarcinoma. Carcinoma was confined to the mucosa or muscularis (early carcinoma) in 5 cases (50%). The prognosis was good in the patients with early carcinoma, but very bad in advanced cases. In conclusion, unsuspected GB carcinoma was incidentally found in 1.89% of GBs removed for benign biliary disease and a considerable number of these unsuspected cases have an early carcinoma.