OBJECTIVE: To assess prevalence and correlates of family caregiver burdens associated with mental and physical conditions worldwide. METHODS: Cross-sectional community surveys asked 43,732 adults residing in 19 countries of the WHO World Mental Health (WMH) Surveys about chronic physical and mental health conditions of first-degree relatives and associated objective (time, financial) and subjective (distress, embarrassment) burdens. Magnitudes and associations of burden are examined by kinship status and family health problem; population-level estimates are provided. RESULTS: Among the 18.9-40.3% of respondents in high, upper-middle, and low/lower-middle income countries with first-degree relatives having serious health problems, 39.0-39.6% reported burden. Among those, 22.9-31.1% devoted time, 10.6-18.8% had financial burden, 23.3-27.1% reported psychological distress, and 6.0-17.2% embarrassment. Mean caregiving hours/week was 12.9-16.5 (83.7-147.9 hours/week/100 people aged 18+). Mean financial burden was 15.1% of median family income in high, 32.2% in upper-middle, and 44.1% in low/lower-middle income countries. A higher burden was reported by women than men, and for care of parents, spouses, and children than siblings. CONCLUSIONS: The uncompensated labor of family caregivers is associated with substantial objective and subjective burden worldwide. Given the growing public health importance of the family caregiving system, it is vital to develop effective interventions that support family caregivers.