A prototype is a theoretical standard against which real people can be evaluated. To derive a prototype of a lonely person, 40 students were asked to describe a lonely person whom they knew. All descriptions were studied by judges who formed a final listing and frequency of all identified features. The 18 features which formed the prototype fell into three categories: feelings of isolation, actions resulting in isolation, and paranoid feelings. The UCLA Loneliness Scale was administered to college students who were then identified as lonely or non-lonely. Previous research on interpersonal problems reported by persons seeking psychotherapy provided a list of problems which subjects card-sorted as familiar or unfamiliar problems. The socializing cluster of problems differentiated between lonely and non-lonely persons. The lonely person prototype also indicated that lonely persons lacked the social skills necessary for making friends. Questionnaire responses of lonely and non-lonely subjects revealed that lonely subjects explained interpersonal failure by a lack of ability. Lonely subjects also scored poorly on a test of interpersonal competence. The findings suggest that lonely persons' self-evaluations of their poor social skills are accurate. (Author/NRB)