This study examined a threshold model that proposes that social support exhibits a curvilinear association with adjustment and distress, such that support in excess of a critical threshold level has decreasing incremental benefits. Women diagnosed with a first occurrence of breast cancer (N = 154) completed survey measures of perceived support (Social Provisions Scale), quality of life (Functional Living Index--Cancer), adjustment (Psychological Adjustment to Illness Scale) and psychological distress (Brief Symptom Inventory) approximately 3 weeks after surgical treatment and 8-16 months later. Consistent with a threshold model, multiple regression analyses suggested a significant curvilinear relationship between social support and distress at Time 1 and Time 2 and between social support and adjustment at Time 2. Consistent with this model, the significant bivariate correlations between social support and outcomes were accounted for almost entirely by women in the lowest quartile of support. Social support among women in the highest 3 quartiles was unrelated or only marginally related to adjustment and distress. (Contains 1 footnote, 4 tables, and 2 figures.)