Potential risk-factors for the acquisition of imipenem-resistant Acinetobacter baumannii were investigated in a cohort study in 25 Spanish hospitals. The clonal relationship among isolates was determined by pulsed-field gel electrophoresis (PFGE). In total, A. baumannii was isolated from 203 patients, with imipenem-resistant (MIC90 128 mg/L) isolates being obtained from 88 patients (43%), and imipenem-susceptible isolates from 115 patients (57%). A wide clonal distribution was observed among the imipenem-resistant isolates, but spread of the same clone among centres was not demonstrated. The results indicated that imipenem-resistant A. baumannii is a widely distributed nosocomial pathogen in Spain and reaches an alarming frequency in some centres. Independent risk-factors for the acquisition of imipenem-resistant A. baumannii were a hospital size of > 500 beds (multivariate OR, 6.5; 95% CI, 1.8–23), previous antimicrobial treatment (multivariate OR, 4.3; 95% CI, 1.6–11), a urinary catheter (multivariate OR, 2.7; 95% CI, 1.1–6.7) and surgery (multivariate OR, 2; 95% CI, 1.07–3.8).