Thirty families with two or more children, one of whom had insulindependent diabetes, were studied to test the effects of communicative functioning on the children's knowledge about diabetes, siblings' perceived responsibility for the diabetic child's care, the children's self-concepts, and the stress felt by each family member. The hypotheses, derived from family systems theory, were that families with "functional" communication patterns would score higher on the first three variables and lower on the last than "dysfunctional" families. After families were videotaped interacting on four tasks, two raters scored the communication patterns. The hypotheses were only partially borne out. Mothers and both children in "functional" families felt less stress. Family functioning was also weakly related to siblings' knowedge about diabetes.This study explored patterns of communication in 30 families with two or more children, one of whom had insulin-dependent diabetes. The goal was to discover relationships between patterns of communication and outcome variables which, according to family systems theory, might be influenced by the way family members communicate with one another. These variables included: siblings' and diabetic children's knowledge about diabetes, siblings' perceived responsibility for the diabetic child's care, and siblings' and diabetic children's self-concepts. The final variable considered was family stress as perceived by the children, their mother and father, and the family as a whole. Relationships among the variables were then analyzed for their implications for diabetes management. The essentials of diabetes management have been recently summarized in this journal by Anderson and Kornblum (3).