BACKGROUND:Depression is highly prevalent among people with MS, and determinants thereof would be useful. OBJECTIVES:We examined the relationship of demographic and clinical factors with positive depression-screen and change in depression over 2.5 years in people with MS. METHODS:Positive depression-screen assessed by Patient Health Questionnaire (PHQ)-2 and PHQ-9. Associations of demographic and clinical factors with depression-screen and change thereof assessed using multivariable regression models, adjusted for age, sex, disability, fatigue, antidepressant use, and baseline PHQ-2, as appropriate. RESULTS:Overweight/obese BMI, comorbidity number, fatigue, and disability were associated with positive depression-screen, while married/partnered state, being employed, higher perceived socioeconomic status, and greater education were inversely associated with depression-screen. After adjustment, only marital status, socioeconomic status, antidepressant medication use, and fatigue were associated with risk of newly positive depression-screen. MS type, relapse number and immunomodulatory medication use were not associated with depression-screen after controlling for disability and fatigue. CONCLUSION:In a large prospective cohort study of depression in people with MS, we substantiated several potential determinants of a positive depression-screen and depression trajectory, particularly fatigue. Given that fatigue is the most common and most significant clinical symptom for people with MS, efforts to reduce fatigue may have follow-on benefits for reducing depression.