Ultrasonography has led to an increase in the incidence of acute acalculous cholecystitis (AAC). Fifty-three patients with AAC are compared to 521 patients with acute calculous cholecystitis (ACC), both out of a series of 2,800 patients operated on between 1970 and 1988. Patients with AAC are usually older males with a high incidence of diabetes mellitus. Over 10% report recent preoperative extrabiliary surgery or trauma, 5 % had undergone splenectomy for hematological indications. Gangrenous changes and obstructive jaundice are significantly more frequent among AAC patients. The bacterial flora, the antibiogram and the incidence of common bile duct stones do not differ between AAC and ACC patients. Early surgery, feasible today with early diagnosis by ultrasonography, gives excellent results in terms of morbidity and mortality. Our series demonstrates low mortality rates for AAC patients when compared to historical series and thus represents, in our opinion, the present trend of change in this group of patients.