Abstract An attempt has been made to relate individual differences in the smoking of cigarettes and in over-eating to the personality dimensions of extraversion and neuroticism. It was postulated and has been experimentally confirmed that extraverts indulge in smoking and over-eating to a greater extent than do more introverted people, the relationship between these two continuous variables being a monotonic one. It was hypothesized that this might be due to the postulated “stimulus hunger” of the extravert, consequent upon the greater degree of cortical inhibition which has often been found to be associated with high degrees of extraversion. It was also postulated that as nicotine is a C.N.S. stimulant drug it would have beneficial effects in people high on neuroticism only if they were also extraverted; if they were introverted it was hypothesized that the effects would be detrimental. The prediction was made, therefore, that neuroticism as such would not be related to smoking and this prediction was, in fact, borne out. Lastly, it was suggested that the giving up of smoking might lead to a greater degree of eating by substituting food for cigarettes in alleviating the stimulus hunger of the subjects in question.