A patient who has attempted suicide presents the physician with an extremely important question, "What should be his action to prevent a possibly successful suicide in the immediate future?" This study was undertaken to obtain data that might help the physician decide what action to take. Specifically the following questions were investigated. What is the incidence of successful suicide following an unsuccessful suicide attempt, as ascertained by a short-term follow-up? What important clinical characteristics of the patient who has attempted suicide help in deciding whether he will be a serious suicidal risk in the near future? In this connection, is it important to make a diagnosis? Are the patient's statements reliable guides to what he will do in the near future? Do patients inform the physician (or someone close to them) of suicidal thoughts or plans often enough to permit preventive action? Is hospitalization necessary for most of these patients?