We studied a group of HIV-infected homosexuals who participated in the Amsterdam Cohort Study on HIV and AIDS to investigate whether greater exposure to sunlight is associated with a less favorable course of some important immunological parameters. This was done because ultraviolet radiation (UVR) is potentially harmful to the cellular immunity and may enhance viral replication. The exposure to UVR was estimated by means of a 2-year retrospective questionnaire in 1997. Both a 2-year cumulative estimate and estimates by 3-monthly episodes were calculated. The associations with CD4+ T-cell count, CD4+/CD8+ T-cell ratio, and T-cell reactivity were investigated. First, the associations between the cumulative estimate and the individual slopes of these parameters during the 2 years covered by the questionnaire were explored by means of a robust regression analysis. Secondly, the short-term association with the estimate by episode was examined by means of a linear mixed-effect model for repeated measurements (LME). No statistically significant associations with the cumulative estimate were found. Although a trend to lower values of the immunological parameters studied after short-term greater exposure in the LME model was observed, the differences were not statistically significant either. These findings suggest that exposure to sunlight does not have a suppressive effect on the above mentioned immunological parameters in HIV-infected persons.