Three out of 2,412 consecutive HIV-infected patients hospitalized since 1990, developed Agrobacterium radiobacter septicemia. All patients were severely immunocompromised, showing a prior diagnosis of AIDS, concurrent opportunistic infections, a mean CD4+ lymphocyte count below 100 cells/microL, and neutropenia. Nosocomial A. radiobacter sepsis occurred in two cases of three, and was related to a lower neutrophil and CD4+ cell count. Antibiotic and cotrimoxazole treatment were carried out during the month preceding disease onset by two and three patients, respectively. Antimicrobial susceptibility assays showed resistance to ureidopenicillins and aztreonam, and complete sensitivity to carbapenems, amikacin, and ciprofloxacin. A therapeutic regimen including amikacin plus ceftriaxone or ceftazidime obtained clinical and microbiological cure in all cases, in the absence of related mortality or relapses. Only two episodes of HIV-associated A. radiobacter complications have been described to date: one case of sepsis and one patient with pneumonia. Despite their low frequency, gram-negative non-fermenting bacilli should be considered in HIV-infected patients with a suspected bacterial complication, because of their cumbersome identification procedures, and their unpredictable antibiotic susceptibility, with elevated resistance to many compounds expected to be effective against gram-negative organisms. A. radiobacter may play a pathogenic role in patients with advanced HIV disease, even when some commonly recognized risk factors are lacking (in-dwelling catheters and instrumentation), while a very low CD4+ lymphocyte count, leukopenia-neutropenia, hospitalization, and concurrent AIDS-related infectious complications, may act as predisposing factors.