Acinetobacter calcoaceticus is widely prevalent in nature and frequently is a commensal in humans. In recent years, however, infections due to this organism are considered to occur more frequently than commonly appreciated, especially among seriously ill hospitalize patients. A spectrum of clinical infections due to A. calcoaceticus seen in 119 patients at Seoul National University Hospital over a one-year period is presented through at retrospective review of 242 patients with Positive culture for A. calcoaceticus. The results are as follows. 1) Most frequent type of specimens from which A. calcoaceticus was isolated was sputum(37%) followed by pus(30%), urine(24%), and blood(9%) in decreasing order of frequency. 2) Other organisms were isolated in combination with A. calcoaceticus in 40% of the infoctions. 3) According to Glew's diagnostic criteria, 119(49%) out of 242 patients were diagnosed as significant clinical infection due to A. calcoaceticus. Most frequent type of significant acinetobacter infection was pulmonary(35%) and urinary(35%) followed by wound infection(27%) and septicelaia(3%). 4) Virtually all of the patients had one of more underlying diseases or predisposing factors; prior antibiotic therapy(79%), instrumentation(11%), local trauma and disease(53%) and surgery (49%). 5) Mortality rate ascribed to A. calcoaceticug infection was 7% and especially high mortality was encountered in patients with pneumonia (l7%). 6) Antibiotic sensitivity test revealed relatively high susceptibility of A. calcoaceticus to gentamicin and claforan (HR 756), however the sensitivity pattern was quite variable among different strains of A. calcoaceticus.