This study examined the relation between children's peer relationships and teacher-rated psychological adjustment. A number of shortcomings in the peer literature were addressed by: (a) employing carefully delineated peer variables (passive isolation, rejected isolation, aggressive-disruptive, peer preference, mutual friendship); (b) employing a data analytic strategy that permitted simultaneous examination of main effects of and interactions among peer variables; (c) using an outcome measure that is well-normed for children and widely used in studies of adjustment; and (d) controlling for outcome measures' autocorrelations across time points. For 236 school children in the third, fourth, and fifth grades, concurrent associations were examined between these peer variables and internalizing and externalizing problems. Longitudinal associations were examined over a period of 2 years. In so doing, we found that passive isolation was a risk factor for internalizing problems, and rejected isolation was marginally predictive of externalizing problems. Furthermore, we found complex moderating effects of mutual friendship, such that children who were not isolated may derive benefits from having a close mutual friend, but the results were not clear for children with poor peer-group relationships. Much additional research is needed to further clarify these findings.