Aim of the study: The aim was to determine the blood concentrations of hydroxychloroquine in Moroccan systemic lupus erythematosus patients and identify the factors associated with interindividual variation. Methods: A cross-sectional study enrolled patients with lupus erythematosus. We recorded demographic features of patients and main clinical and biological characteristics of the disease. We determined the blood concentrations of hydroxychloroquine for the entire patient enrolled in this study by liquid chromatography – mass spectrometry. Patients were divided according to their blood hydroxychloroquine level into three groups: low blood concentration (<500 ng/mL), therapeutic range (500-2000 ng/mL) and high blood HCQ concentration (>2000). Results: Eighty subjects were included; 77 were female and the mean age was 36.9±12, 2 years. The median concentration of hydroxychloroquine was 830 ng/mL (range: 35-3,200 ng/mL); 13 patients (16%) had low blood levels, 59 (74%) were in therapeutic range while 8 (10%) had high blood concentrations. Low body mass index and the use of corticosteroids were associated with high hydroxychloroquine concentrations (p=0.03 and p=0.02 respectively). Conclusion: We report for the first time the blood concentration of hydroxychloroquine in Moroccan lupus patients and we found significant variability between patients for the same dose. Various factors affected this concentration and further studies are needed to expand the sample.