Forty consecutive patients with nosomial infections caused by multidrug-resistant Acinetobacter baumannii were treated with intravenous ampicillin/sulbactam. The infections were primary bloodstream (32.5%), pneumonia (30%), urinary tract (15%), peritonitis (7.5%), surgical site (7.5%), meningitis (5%) and sinusitis (2.5%). Most were severe infections with underlying conditions (median APACHE II score: 14.5) and 72.5% occurred in the ICU. Twenty-seven (67.5%) were improved/cured, seven (17.5%) were failures and six (15%) were considered to have an indeterminate outcome because patients died within the first 48 h of treatment. Two cases of meningitis were treated and did not respond. The median daily dose of ampicillin/sulbactam was 6 g/3 g and six patients received 12 g/6 g. No adverse effects were observed. This study indicates that ampicillin/sulbactam may be a good and safe therapeutic option to treat severe nosocomial infections caused by multi-drug resistant A. baumannii.