Yellow oleander or Thevetia peruviana is a very common plant in the North of Sri Lanka. Ever since the fact that the fruits and kernel are poisonous was published in the Newspapers, many cases of poisoning due to Thevetia occurred. 170 cases of Thevetia poisoning admitted to the Teaching Hospital, Jaffna in the North of Sri Lanka are studied by the authors. The mortality, morbidity, age distribution, presenting symptoms and clinical findings are analysed. The action of the cardiac glycoside in Thevetia is clearly demonstrated in this study.