Description: Background: Ingestion of pesticides (mainly paraquat) accounted for one-fifth of suicides in South Korea in 2006–10. We investigated the effect on suicide mortality of regulatory action, culminating in a ban on paraquat in South Korea in 2011–12. Methods: We calculated age-standardized method-specific suicide mortality rates among people aged ≥15 in South Korea (1983–2013) using registered death data. Negative binomial regression was used to estimate changes in the rate and number of pesticide suicides in 2013, compared with those expected based on previous trends (2003–11). Results: Pesticide suicide mortality halved from 5.26 to 2.67 per 100 000 population between 2011 and 2013. Compared with the number expected based on previous trends, the regulations were followed by an estimated 847 [95% confidence interval (CI) –1180 to –533] fewer pesticide suicides, a 37% reduction in rates (rate ratio = 0.63, 95% CI 0.55 to 0.73) in 2013. The decline in pesticide suicides after the regulations was seen in all age/sex/geographical groups. The absolute reduction in the number of suicides was greatest among men, the elderly and in rural areas. The reduction in pesticide suicides contributed to 56% of the decline in overall suicides that occurred between 2011 and 2013. There was no impact of the regulations on crop yield. Conclusions: The regulation of paraquat in South Korea in 2011–12 was associated with a reduction in pesticide suicide. Further legislative interventions to prevent the easy availability of highly lethal suicide methods are recommended for reducing the number of suicides worldwide.