We analyzed the influence of temperature, humidity, and atmospheric pressure on the 1-year incidence of nephrolithiasis among human immunodeficiency virus type 1-infected patients treated with indinavir. One hundred three patients (13.6%) developed 326 episodes of nephrolithiasis. Eighty-two patients (79.6%) had more than one episode (range, two to seven episodes). The overall incidence ranged from 0 to 10.2 episodes per 100 patients exposed per month. There was a significant correlation between temperature and the overall incidence of nephrolithiasis and the incidence of recurrences but not with the incidence of first episodes. Nephrolithiasis was not related to humidity or atmospheric pressure. Our data support the standard recommendation of drinking at least 1.5 L of water daily to prevent nephrolithiasis in most patients treated with indinavir irrespective of meteorologic factors. However, the risk of nephrolithiasis is higher for a certain subgroup of patients when the environment is hot irrespective of adequate water intake.