Each year, 14,000 children are diagnosed with cancer in the United States. Prolonged, intensive treatment regimens disrupt the entire family system, but effects on siblings are poorly understood. In this preliminary investigation, we employed a risk and resistance framework to study adjustment among 30 siblings (aged 10-17) of children undergoing cancer treatment. We examined whether or not objective stress associated with the cancer experience (contextual threat) predicted sibling distress and explored demographic and disease-related predictors of sibling adjustment. Contextual threat was positively associated with sibling-reported distress, independent of sibling age, gender, birth order relative to the child with cancer, and cancer treatment intensity. From among the demographic and disease-related factors, only younger birth order relative to the child with cancer was independently associated with sibling distress. These results suggest that a subset of siblings may be at increased risk for elevated distress in the face of their brother's or sister's illness.