Study Objective: Data on poisoning with MCPA (4-chloro-2-methylphenoxyacetic acid) is limited to six case reports. Our objective is to describe outcomes from intentional self-poisoning with MCPA in a prospective case series of 181 patients presenting to hospitals in Sri Lanka.Methods: Patient information was collected by on-site study doctors as part of an ongoing prospective cohort study of poisoned patients. History, clinical details and blood samples were obtained prospectively.Results: Overall clinical toxicity was minimal in 85% of patients, including mild gastrointestinal symptoms in 44% of patients. More severe clinical signs of chlorophenoxy poisoning reported previously such as rhabdomyolysis, renal dysfunction and coma also occurred, but were uncommon. Eight patients died (4.4%). Most deaths occurred suddenly from cardiorespiratory arrest within 48 hours of poisoning; the pathophysiological mechanism of death was not apparent. The correlation between admission plasma MCPA concentration and clinical markers of severity of toxicity (physical signs, symptoms and elevated creatine kinase) was poor.Conclusions: Intentional self-poisoning with MCPA generally causes mild toxicity, but cardiorespiratory arrest and death may occur. All patients should receive routine resuscitation and supportive care. It seems reasonable to correct acidosis and maintain an adequate urine output, but there is insufficient evidence to support other specific interventions. Our data do not support a clinical role for measurement of plasma MCPA in the acute management of poisoning and insufficient data were available to fully examine the utility of measured electrolytes and creatine kinase.