The aim of the present study was to examine the effect of HIV infection on odour memory. Recognition and identification olfactory tests were administered to six groups of patients defined according to a decrease in cellular immunity: asymptomatic HIV seropositive (HIV+), symptomatic HIV+, HIV+ AIDS, and three groups with a mild, moderate, and severe degree of dementia (AIDS dementia complex [ADC]). Consistent with the literature, the general results show that HIV infection is associated with a decrease in olfactory ability. In addition, a polynomial linear trend analysis indicates a constant decrease in performance from the first to the sixth group of patients, related to the number of CD4 T lymphocytes circulating and to the severity of the pathology. An interesting result regards the drop in performance exhibited by ADC patients on the identification task. Reasonably, such an effect is not attributable to a decline in olfactory ability only, bit rather to a severe semantic memory deficit. It follows that the two tasks used here can be useful clinical supports to discriminate between the mental operations involved in a low cognitive demand task (recognition) and in a high cognitive demand task (identification).