To examine these associated factors and outcomes, we carried out the Thai Study of Affective Disorder (Thai-SAD), a one-year observational, collaborative, prospective cohort study of treatment outcomes in patients with MDD and/or dysthymic disorder, as well as patient quality of life. The research consisted of a multicenter study carried out at psychiatric outpatient clinics at tertiary hospitals (university and provincial hospitals) throughout Thailand, using newly diagnosed or referred cases from community hospitals and primary care settings. The purpose of this paper is to present the baseline sociodemographic and psychosocial characteristics of the study participants.