Objective This study aimed to assess the sleep quality and the factors affecting the sleep quality in patients with SLE. Methods This was a descriptive and cross-sectional study conducted in 105 patients with SLE who were admitted to the rheumatology polyclinic of a university hospital between May and July 2017. The data were collected using a "Patient Description Form" and the "Pittsburgh Sleep Quality Index (PSQI)." Results The total mean (standard deviation) PSQI score of the patients was 7.81 (3.11). Duration of disease, presence of comorbid diseases, side effects of drugs, and sleep disruption and related problems were identified as factors affecting sleep quality. The model of the regression showed that side effects of drugs, sleep disruption, and trouble falling asleep suffered higher PSQI score (bad sleep quality). Conclusions Results of this study showed that the sleep quality was generally poor in patients with SLE. Sleep quality was affected by some disease and sleep variables. Therefore, comprehensive sleep evaluation is necessary in the planning of treatment and care of SLE patients and to implement initiatives to improve sleep patterns in these patients.