Objective Concerns about the affordability of medications are common in systemic lupus erythematosus (SLE), but the relationship between medication cost concerns and health outcomes is poorly understood. We assessed the association of self-reported medication cost concerns and patient-reported outcomes (PROs) in a multiethnic SLE cohort. Methods The California Lupus Epidemiology Study is a cohort of individuals with physician-confirmed SLE. Medication cost concerns were defined as having difficulties affording SLE medications, skipping doses, delaying refills, requesting lower-cost alternatives, purchasing medications outside the United States, or applying for patient assistance programs. Linear regression and mixed effects models assessed the cross-sectional and longitudinal association of medication cost concerns and PROs, respectively, adjusting for age, sex, race and ethnicity, income, principal insurance, immunomodulatory medications, and organ damage. Results Of 334 participants,