Objective. To determine the impact of the patient's sex on the manifestations and outcome of systemic lupus erythematosus (SLE). Methods. We studied SLE patients who were ages 16 years or older and had a disease duration of ≤5 years at the time of enrollment in the LUpus in Minorities, NAture versus nurture cohort, a multiethnic cohort consisting of Hispanic, African American, and Caucasian patients. Socioeconomic/demographic, clinical, and serologic features, as well as disease activity (by the Systemic Lupus Activity Measure, Revised) and damage accrual (by the Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index) were compared between male and female patient groups. Multivariable analyses using male sex and damage accrual as dependent variables were then performed. Results. Sixty-three male SLE patients (10.2%) from all ethnic groups were included. The mean ages of the male and female patients were comparable. Factors that were either more frequent or tended to be more frequent among male SLE patients were Caucasian ethnicity, smoking, alcohol use, lupus anticoagulant (LAC) positivity, and renal involvement, whereas musculoskeletal involvement was less common. American College of Rheumatology criteria accrual time and disease duration were shorter in the male patients; damage was more common and of higher magnitude in this group. LAC positivity, shorter disease duration, and higher early damage scores were independently associated with male SLE. Male sex was a strong predictor of baseline damage, measured as a categorical variable (t-test = 2.357, β-standardized coefficient 0.113; P = 0.019) or a continuous variable (hazard ratio 3.179 [95% confidence interval 1.999-5.056]; P < 0.001). Male sex was also positively associated with the development of damage over most of the course of the disease. Conclusion. Poorer long-term prognosis among men with SLE appears to be decisively determined by their accelerated development of damage, particularly early in the course of the disease. © 2007, American College of Rheumatology.