Background. Legislation requiring the addition of bittering agents to antifreeze enables assessment of the impact on frequency, volume and severity of suicidal antifreeze ingestions. Methods. U.S. poison control data were analyzed comparing 130 suicidal antifreeze ingestions occurring in two states after enactment of bittering requirements with 3,493 cases occurring in states (or at times) where bittering was not required. Results. The frequency of suicidal antifreeze ingestions was unchanged after implementation of bittering. The volume implicated, medical outcome distribution, and use of antidotes, hemodialysis, intubation, or critical care, showed no significant difference between bittered and non-bittered groups. Bittering was not a significant contributor (positively or negatively) in predicting lethal or life-threatening medical outcomes. Conclusion. The addition of bittering agents to antifreeze for the purpose of limiting the frequency or severity of suicidal ingestions could not be justified using U.S. poison control data.