Research has suggested that the incidence of loneliness peaks at adolescence and decreases with age. Changes in the determinants of loneliness during adolescence were investigated for grade 8, grade 11, and university students. Subjects (N=410) completed a written questionnaire which included ten items from the UCLA Loneliness Scale, the Self-Esteem Scale, a self-consciousness sub-scale, and items from the Ego Identity Scale. Subjects also reported on their number of friends and frequency of contact, and completed an adapted version of the Friendship Scale. Other questions measured each subject's relationship with family and parents, examined personal and social factors associated with loneliness, and recorded demographic and situational factors. Results indicated no significant differences in the amount of loneliness among the three age groups. Some determinants (self-esteem, social anxiety, level of identity achievement, quality of the family relationship, satisfaction with friendship relations) were strong predictors of loneliness for all groups, while others changed with age. For the youngest group, the quality of the relationship with the mother was a particularly strong predictor. For older adolescents the frequency of contact with friends and satisfaction with dating relationships were more important predictors of loneliness. The findings tend to provide some support for the definition of loneliness as a social deficiency. (Author/NRB)