Relationship between zoster and seropositivity for HIV is studied. Serum samples from 66 patients presenting acute zoster infection were tested for HIV antibodies, using ELISA. There was no previous selection of patients, what rendered the population studied unbiased. Seven patients (10.6%) were positive for HIV antibodies. Among them six belonged to AIDS risk groups, all were males and six had ages between 19 and 39 years (mean age value 31.7). Results suggest that the finding of zoster in younger age groups is not necessarily linked to HIV infection. When zoster is diagnosed in patients who belong to AIDS risk groups, independently from their age, the association with HIV infection is statistically significative. In these cases zoster can even be considered as a marker for HIV infection and it is mandatory to test these patients for HIV antibodies.