BACKGROUND: As the proportion of elderly people within a population increases there is an accompanying increase in the role of informal caregivers. Many studies on caregivers report negative health outcomes but very few have addressed positive aspects of caregiving. This study examines characteristics of Thai caregivers, the distribution of psychological distress and mental health among caregivers, and the association between caregiver status and psychological distress. METHODS: This report is based on an ongoing national cohort study of 60,569 Thai adults. Caregiving was common in the cohort, and in 2009 6.6% were full-time and 27.5% were part-time caregivers. Outcomes of the study were reported using an international standard Kessler 6 for psychological distress and a national Thai Mental Health Indicator. Determinants included age, sex, marital status, household income, work status and urban-rural residence. Frequency of social contacts was also included as explanatory variable. RESULTS: Among cohort members, 27.5% were part-time caregivers and 6.6% were full-time caregivers. Compared to non-caregivers, full-time caregivers tended to be older, to be married, more likely to be in the lowest household income group, to be unpaid family members, and to reside in rural areas. We noted the seeming contradiction that when compared to non-caregivers, the caregivers reported higher psychological distress but higher positive mental health (i.e., self-esteem and content with life), higher positive mental capacity (i.e., coping with crises), and higher positive mental quality (i.e., helping others). After adjusting for possible covariates, part-time and full-time caregivers were more likely to report high psychological distress (Adjusted Odds Ratios, AOR 1.33 and 1.78 among males and 1.32 and 1.45 among females). Less contact with colleagues was associated with high psychological distress both in males and females (AOR 1.36 and 1.33). Less contact with friends was also associated with high psychological distress, especially among females (AOR 1.27 and 1.42). CONCLUSIONS: This study highlights caregivers in Thailand, the strong possibility of mental health benefits, some risks of associated psychological distress, and the positive role of keeping social contacts. Early identification of vulnerable caregivers is required to target effective health promotion.