A retrospective study was carried out to evaluate the incidence, etiology and role of non-opportunistic bacterial infections in a series of 788 consecutive HIV-infected patients hospitalized during the last 7 years; 71.9% of patients were i.v. drug addicts, 15.6% homo-bisexual men, 7.4% heterosexuals, 2.7% haemophiliacs and 2.4% children with vertically-acquired infection. According to the CDC classification of HIV infection, 71 patients were classified as CDC I-II, 148 as CDC III, and 569 (72.2%) as CDC IV. Diagnosis of bacterial infection was based on signs and symptoms, in association with the isolation of microorganisms consistent with the clinical picture. Two hundred and nineteen patients out of 788 (27.8%) (4 in CDC group I-II, 34 in CDC III and 181 in CDC IV), presented one or more episodes of non-opportunistic bacterial infection. The morbidity of these infections showed a significant correlation with the progression of HIV disease (CDC III vs. CDC I-II [p < 0.003] and CDC IV vs. CDC III [p < 0.05]), but no significant relation was found with age, sex or type of risk for HIV infection. The most frequent clinical picture was sepsis/bacteraemia (33.3%), followed by respiratory tract (23.8%), and genitourinary tract (20.8%) infections. A total of 399 bacterial pathogens were isolated in 303 different episodes of infection: 211 (52.9%) were gram-positive and 188 gram-negative, with Staphylococcus aureus (69 isolations), Staphylococcus epidermidis (50), and Pseudomonas spp. (48) as the major pathogens. Sepsis/bacteraemia was the most frequent clinical picture associated with growth of gram-positive pathogens, while detection of gram-negative bacteria appeared more significantly related with genitourinary or respiratory tract localizations. Bacterial infections in hospitalized HIV-infected patients, even though rarely life-threatening, need particular attention because of the high incidence and recurrence rate, the wide aetiological and clinical spectrum, the frequent microbial associations and the strict relationship with the progression of HIV disease.