The authors investigated the relative contribution of peer relations, family structure, and demographic variables in predicting loneliness in adolescents. Ninth-grade high school students (N = 756) from 8 different schools representing various socioeconomic status in Ankara, Turkey, completed the UCLA Loneliness Scale (D. Russell, L. A. Peplau, & M. L. Ferguson, 1978), the Family Structure Assessing Instrument (A. Gulerce, 1996), and an author-constructed questionnaire involving demographic information and variables on peer relations. Results of multiple regression analyses indicated that all three sets of variables accounted for 41% of the variance in loneliness scores. Additionally, peer relations contributed 34% of the variance, family structure 14%, and demographic variables 3%. Within the limits of the study, peer relations appear to be the best predictors of adolescent loneliness.