This multi-institutional study investigated the association of behavioral/emotional adaptation among siblings of children with cancer with maternal general well-being, physical health, and resource use. One hundred seventy siblings and mothers completed standardized interviews and self-report measures 6 to 42 months after the cancer was diagnosed. As a group, mothers of children with cancer reported significantly lower levels of well-being than matched controls. When stratified according to the level of the sibling's behavioral/emotional adaptation, mothers of siblings in the Dysfunctional group (1) reported the lowest levels of well-being; (2) during the preceding year, were more likely to have sought professional services than mothers of children in the Resilient group; and (3) were least likely to have found social support helpful. Our results support an association between maternal well-being and sibling adjustment but show it is unlikely that nonspecific social support will improve adjustment. The rationale for problem-solving training for mothers is provided.