Abstract Background A relationship between happiness and mortality might seem obvious, but outside of affluent settings in developed countries there is almost no actual evidence that this is so. Findings We report our findings on happiness and mortality in Buddhist Southeast Asia. Our data are derived from a prospective nationwide cohort study of 60,569 Thai adults reporting in 2009 and followed up for all-cause mortality over the next four years (296 deaths). We also gathered data on a wide array of covariates and included these in the final model of the unhappiness-mortality effect. All final effect estimates were mutually adjusted odds ratios (AOR) and cohort members who reported being happy ‘little’ or ‘none of the time’ in 2009 were more likely to die (AOR 2.60, 95% Confidence Interval 1.17-5.80). Other significant covariates include being female (