Alternate explanations of loneliness proposed by Weiss (1973)—the situational theory and the characterological theory—were tested in samples of early (N =113), middle(N =106), and late(N =106) adolescents. In addition to completing the Revised UCLA Loneliness Scale, participants completed instruments linked to either the situational or characterological explanation of loneliness. Data were analyzed using hierarchical analysis of sets. For early adolescents, the results indicated that the characterological set of variables explained somewhat more variance in loneliness than did the situational set of variables. These findings did not replicate those of the original study (Mahon & Yarcheski, 1988). For middle and late adolescents, the results indicated that the situational set of variables explained more variance in loneliness than did the characterological set.