Four studies are reported in which an interview or questionnaire is used to measure the relation between behavioral inhibition, defined as consistent restraint in response to unfamiliar social or nonsocial stimuli, and adult mental health. In Study 1, undergraduates were tested using a retrospective self-report questionnaire. Those who reported more behaviors suggesting childhood inhibition also reported more mental health problems. Study 2 was an attempt to establish the postdictive validity of the measurement of childhood inhibition. College students and their parents completed the questionnaire independently and were in extremely strong agreement regarding the student's inhibited behaviors as a child. In Study 3, self-reported contemporary behaviors suggesting inhibition correlated with the retrospective self-report of inhibition. Both measures correlated with the State Anxiety Subscale of the State-Trait Anxiety Inventory and the Center for Epidemiologic Studies Depression Scale, and both accounted for unique variance in anxiety, but only contemporary inhibition accounted for unique variance in depression. In Study 4, adults who had been treated for panic disorder or depression were interviewed and reported more behaviors indicative of inhibition during childhood than did control subjects. These four studies support the usefulness of retrospective self-report as a measure of childhood inhibition and are compatible with the hypothesis that a tendency toward inhibited behavior in childhood or adulthood may be a risk factor for mental health problems.