Thirty-six hospitalized patients who were considered by emergency room physicians to have ingested medically serious tricyclic overdoses were studied. The purpose of the project was to determine if psychiatric daignosis and associated psychiatric factors correlated with the severity of the overdose as defined by plasma drug levels. Medically serious overdoses were ingested by patients with alcoholism, primary affective disorder, undiagnosed psychiatric illness, and Briquet's syndrome. Prior psychiatric treatment, prior admissions, prior overdoses, or precipitating events did not correlate with the medical severity of the ingestion. Attempting to predict the individual medical severity of the overdose from psychiatric factors resulted in a dangerous underestimation of the risk for patients with Briquet's syndrome and an overprediction in the case of primary affective disorder.