In order to verify the accuracy of the commonly used statement, "I sweat blood," a survey of the literature in the subject of hematidrosis was made. Seventy-six cases were studied and classified into categories according to the causative factor. These were, component of systemic disease, vicarious menstruation, excessive exertion, psychogenic, and unknown. The psychogenic were further subdivided into those that occurred only one time, those that recurred and the stigmatics. Acute fear and intense mental contemplation were found to be the most frequent inciting causes. Hematidrosis is an extremely rare clinical phenomenon with only few instances reported to have occurred within the twentieth century.