This paper quantifies the extent of pesticide overuse in vegetable production systems in Southeast Asia. Pesticide overuse was defined as levels of use in excess of an economic (profit-maximizing) optimum. A production function with an exponential damage abatement term was estimated. Data come from a representative sample of 1000 farmers producing leaf mustard and yard-long bean in Cambodia, Laos and Vietnam. The results show that 100% of the sampled farmers in Vietnam, 73% in Cambodia and 59% in Laos overused pesticides. Pesticide expenditure in excess of the economic optimum was 96% for Vietnam, 92% for Cambodia, and 42% for Laos. Pesticide overuse was positively associated with men in charge of pest management decisions, farmers seeking advice from pesticide sellers and a strong belief that pesticides are effective. It was negatively associated with the use of non-chemical methods of pest control. These results imply that farmers in Southeast Asia are spraying excessively and inefficiently and could increase their profits by applying fewer pesticides. •We quantify pesticide overuse in vegetable production in Cambodia, Laos and Vietnam.•Production function with damage control term was estimated with data for 1000 farms.•77% of farmers overused pesticides; 77% of pesticide expenditures are overuse.•Greater overuse was observed among male applicators.•Greater overuse was also observed where pesticide sellers advised farmers.