In immunocompromised or debilitated persons, fungi may become pathogenic and cause serious infection. Gallbladder disease has been associated with fungal infections. In a case presented here, Saccharomyces cerevisiae (brewer's yeast) was the pathogen in calculous cholecystitis in a patient with diabetes mellitus. S. cerevisiae is commonly used for the fermentation of carbohydrates in the production of beer, wine, and bread, and has not previously been reported as a pathogen in acute cholecystitis.