The authors describe three cases of severe accidental poisoning by plants used as part of a traditional treatment in Mayotte. The established, or suspected, toxicity of Thevetia peruviana (Yellow oleander), Cinchona pubescens (Red quinine-tree), Melia azaderach (Persian lilac, also called china berry) and Azadirachta indica (Neem), is discussed. The clinical presentation is cardiac (atrioventricular block) and well known for Thevetia and Cinchona intoxications. Neurological signs and multi-organ failure are found for Azadirachta and Melia. The identification of the plants is never easy, nor is the evidence of their accountability. In the three cases reported, no other cause than the traditional treatment has been found to explain the clinical presentation. The outcome was favorable in all cases. The authors emphasize the difficulties to investigate these accidents, the poor medical knowledge of these practices in tropical areas, and in Mayotte particularly. The need for cooperation with local botanists, familiar with traditional medicine, is also underlined.