Antimicrobial therapy is inappropriate in 9 to 64% of the patients hospitalized. We evaluated the antibiotic use in Internal Medicine wards of an Italian region (Lazio) by a prospective multicenter, observational study. One thousand and nine patients were evaluated. Patients under antimicrobial treatment (PUAT) were 588 (58.2%), patients without treatment (PWT) 421 (41.8%). Infections were classified as community acquired (47.8%), hospital acquired (10.3%) or healthcare-associated (11.4%); the remaining 30.5% of infections did not receive any epidemiological classification. Samples for microbiological examination were collected in 41.6% of PUAT. The antibiotic choice was empiric in 94.8% of the cases and protected penicillins were selected in 48% of the cases. The mean duration of treatment was 9.5±6 standard deviation (SD) days. Only 6% of the patients switched from intravenous to oral therapy. Age, length of hospital stay and mortality were higher for PUAT than for PWT (mean age: 75.9±15 SD vs 74.2±15 SD years, P<0.02; length of hospital stay: 13.7±10.4 SD vs 10±8.4 SD days, P<0.01; mortality: 15.9% vs 3.1%). Antibiotic stewardship needs to be implemented all over the hospitals of Lazio region.