- Nosocomial infections are a major cause of morbidity and mortality among hospitalized patients. The use of new generation antibiotics of wide spectrum caused a higher rate of virulent infections. a) To study the prevalence, pattern and etiology of nosocomial infections in patients hospitalized in departments of internal medicine. b) to determine the characteristics of high-risk patients, deserving special precautions. All medical files of patients who were admitted to internal medicine departments during the years 1994-8 were reviewed. All patients with nosocomial infections were included according to specific criteria. Of 2789 medical files, 72 (2.6%) patients, randomly elected had 76 episodes of nosocomial infection. Urinary tract infection (40.8%), pneumonia (32.9%) and sepsis (9.2%) were the most frequent infections. Mortality was significantly higher in patients with nosocomial infections--48.6% compared to 5% in a control group (p < 0.001). E. Coli, Pseudomonas auroginosa, and Staphylococcus Aureus were the most frequent infecting bacteria. Empiric antibiotic therapy was used in 84.7% of the patients. Any bacterial isolation was found in 61.9% of the patients samples (including blood cultures, urine cultures etc). Old age, female gender, prolonged hospitalization, mechanical ventilation and indwelling urinary catheter were found as risk factors for nosocomial infections. 1. Nosocomial infections in internal medicine departments in Brazilai hospital were found to be less common than previously reported. 2. Five risk factors for nosocomial infections were correlated with a higher prevalence of the disease. 3. Mortality due to nosocomial infections is very common, probably due to inappropriate empiric treatment and high rate of bacterial resistance. 4. Simple preventive measures as well as immediate treatment of nosocomial infection with proper antibiotics are expected to decrease mortality.