In a prospective study of 1,046 male medical students, those who later committed suicide showed a heightened sensitivity in stressful situations as assessed by the Habits of Nervous Tension Questionnaire (HNT). Survival analyses specified 2 of the 25 HNT items as the strongest suicide predictors: Irritability (relative risk 5.5; 95% confidence interval 1.76-17.17) and Urinary Frequency (3.3; 1.07-10.32). No other risk factors for suicide emerged from family background measures or individual medical school measures. It appears that types of sensitivity reflect psychological characteristics that are long-term precursors of suicide.