Approximately 90% calculous; 10% acalculous. Acalculous cholecystitis is associated with higher complication rate and acute illness (i.e., burns, trauma, major surgery), fasting, hyperalimentation leading to gallbladder stasis, vasculitis, carcinoma of gallbladder or CBD, some gallbladder infections (Leptospira, Streptococcus, Salmonella, or Vibrio cholerae), but in >50% of cases an underlying explanation is not found.