To eliminate the influence of other factors, we also analyzed the total number of inpatients each month between January 1997 and December 2006 and calculated the ratio of patients with active SLE relative to the total number of inpatients. We also found that the relative ratio of patients with active SLE was significantly higher in winter than in other seasons. Zhanjiang City is located at east longitude 110.3˚and northern latitude 21.2˚, and has a subtropical climate regulated by the ocean. Based on collected meteorological data, the annual mean temperature is 23.2˚C. In July, the mean temperature is 29.1˚C, there is the most daylight and sunlight intensity is strongest. In January, the mean temperature is 16.6˚C, there is least daylight and sunlight intensity is weakest. In contrast with the traditional viewpoint that the highest incidence of SLE should occur when sunlight and UV rays are strong, our results show that the number of patients with active SLE is fewer in summer when UV rays are stronger, while there is a higher incidence in winter when UV rays are weaker. Our study failed to discover whether various lupus lesions have seasonal distribution; however, Schlesinger et al. 15 found that the incidence of membranous lupus nephritis increased in winter.