ObjectiveAs it is not clear how body-mass index (BMI) may relate to diagnosis, symptom-severity, illness-course, and treatment-response among psychiatric patients, we related BMI to psychiatric diagnosis and to selected clinical and demographic factors in major affective disorder subjects. MethodsWe analyzed mean BMI levels vs. diagnosis, and evaluated selected risk factors for association with overweight and obesity among subjects with DSM-5 major affective disorders. ResultsIn 1884 subjects, BMI ranged from 23.4 kg/m2 with anxiety disorders to 27.6 with psychotic disorders, and averaged 24.1 among 1469 affective disorder subjects. Mood-disorder subjects with BMI ≥ 25 (overweight/obese) were more likely: men, older, married, with more children and siblings, less education, lower socioeconomic status, engaged less in physical exercise, smoked more, and lived in less densely populated areas. They also were more likely to have: BD than MDD, familial mood disorders, no co-occurring ADHD, higher serum triglyceride levels, more time depressed and less improvement in depression ratings with treatment. ConclusionsRisk of being overweight or obese was greatest with psychoses, least with anxiety, personality, and minor depressive disorders, and intermediate with major mood disorders. Several plausible risk factors for high BMI were identified in mood disorder subjects, including male sex and with BD > MDD. Striking were selectively greater prospective morbidity and decreased treatment-response for depression vs. mania with BMI ≥ 25.