Xanthogranulomatous cholecystitis is an uncommon benign thickening of the gallbladder wall characterized histopathologically by extensive histiocytic infiltration. A case is presented in which a 62-year-old woman with clinical cholecystitis was found at surgery to have a markedly thick-walled, adherent gallbladder, raising the differential diagnosis of an inflammatory versus an infiltrating neoplastic process. Intraoperative fine needle aspiration (FNA) biopsy revealed abundant foamy histiocytes ("xanthoma cells"), both dispersed and in clusters associated with capillaries suggestive of organization. Occasional multinucleated giant cells and columnar epithelial cells were also present. The differential diagnosis of histiocytic processes sampled by FNA biopsy is reviewed.