The authors tested whether deficits in perceived social support predicted subsequent increases in depression and whether depression predicted subsequent decreases in social support with longitudinal data from adolescent girls (N = 496). Deficits in parental support but not peer support predicted future increases in depressive symptoms and onset of major depression. In contrast, initial depressive symptoms and major depression predicted future decreases in peer support but not parental support. Results are consistent with the theory that support decreases the risk for depression but suggest that this effect may be specific to parental support during early adolescence. Results are also consonant with the claim that depression promotes support erosion but imply that this effect may only occur with peer support during this period.