Objectives: To evaluate the efficacy and acute side effects of ciprofloxacin treatment in newborns who developed nosocomial Pseudomonas aeruginosa infection. Methods: Intravenous ciprofloxacin treatment was given to 30 newborns who developed nosocomial P. aeruginosa infection as proven by culture antibiogram results. Initial doses of 10 mg/kg/day were given and increased up to 40 mg/kg/day according to clinical response, laboratory and culture results. During therapy, complete white blood cell counts, urinalysis, liver and renal function tests were performed weekly. All patients were examined daily during treatment for possible symptoms of joint toxicity such as erythema and swelling. The patients were evaluated by general physical examination, with special attention to joints, 1 week after discharge. Results: Two of the patients (6.6%) died due to pseudomonas infection, but the bacteria were successfully eradicated in 28 patients (93.4%). Four patients died from other causes. No laboratory abnormality related to ciprofloxacin was observed during treatment. Swelling and hyperemia of the joints were not encountered during treatment and the 1-week period after discharge. Ciprofloxacin-resistant P. aeruginosa isolates were not grown during the study. Conclusion: Ciprofloxacin treatment is effective in life-threatening multi-drug-resistant P. aeruginosa infections. Copyright (C) 2004 S. Karger AG, Basel.