This study investigated the relation of loneliness in middle childhood to behavioral, sociometric, and attributional measures of social functioning. Data for 128 third- through sixth-graders were collected on three occasions during a 1-year span. Teachers completed a rating scale assessing students' social behavior. Children's peer acceptance was assessed using a sociometric rating scale; causal attributions for social rebuke were collected from each child using vignettes; and children's loneliness was assessed using the adapted Asher et al. (1984) loneliness measure. Results indicated that concurrent loneliness was related to withdrawn social behavior, poor peer acceptance, few or no friendships, and an internal-stable attributional style. After prior loneliness was controlled for, no other measures of social functioning predicted loneliness at 10 weeks, but sociometric and attributional measures predicted loneliness at 40 weeks. Loneliness also predicted changes in later social functioning. Analyses indicated that children without friends were lonelier than children with friends, and as time passed, friendless children became more lonely. Findings suggest that loneliness in middle childhood is a stable phenomenon. A list of 31 references is included. (BC)