The risk of urinary infection is more frequent in AIDS-patients than in normal subjects; it is not yet known if the risk is higher in urological patients. We have studied 394 urine cultures of 242 AIDS-patients (CD4 + < 200 cu. mm), aged from 25 to 52 years (mean=35.1; SD=4.72). Results were analyzed and statistically compared with those obtained in similar studies carried out on AIDS and urological patients. On the whole, 52 urine cultures (13.1%) were positive. Etiology was mainly supported by E. faecalis (Gram-positive) and E. coli (Gram-negative). AIDS patients, without urinary catheter, show a higher risk of urinary infection than normal subjects (P<0.02) but lower than urological patients (P=0.000). An increase in the isolation of Gram-positive bacteria and mycetes in comparison with Gram-negative (already observed in urological patients) has been confirmed. Bacteria isolated in AIDS patients showed variations in sensitivity to usual antibiotics.