During the course of a morbidity study in two communities in the town of Croydon, carried out between 1960 and 1962, it proved possible to incorporate an investigation of the shortened version of the Maudsley Personality Inventory (M.P.I.). This twelve-item questionnaire, constructed by Eysenck (1958) for studies of this type, gives measures of neuroticism and extraversion as defined within his personality theory (Eysenck, 1959). Initially the inventory used was identical with that described by Eysenck. After a time (during which test-retest was carried out on 130 adults), however, it was felt that three of the questions relating to extraversion were rather cumbersome, and the following changes were made. Question D, “Are you happiest when you get involved in some project that calls for rapid action?”, was amended to “Are you happiest when you get involved in something that calls for rapid action?”. Question G, “Do you usually take the initiative in making new friends?”, was amended to “Do you usually take the first step in making new friends?”. Question L, “Would you be very unhappy if you were prevented from making numerous social contacts?”, was amended to “Would you be very unhappy if you were prevented from meeting lots of people ?”. It was assumed that these minor alterations would not significantly affect the extraversion scores, and this assumption is borne out by the fact that neither the means of scores nor the test-retest correlations were significantly different on comparison of the two versions. This present study reports the frequency distribution of M.P.I. scores in the population studied and the test-retest reliability of the inventory.