This study of 113 adolescent females with IDDM and their mothers investigated whether: (1) interaction patterns are more dysfunctional in families of girls with eating disturbances than in those without; and (2) the relationship between family functioning and metabolic control is mediated by an eating disturbance. Based on self-reported eating attitudes and behaviors, subjects were categorized as Nondisturbed (N = 56), Mildly Disturbed (N = 37), and Highly Disturbed (N = 20). Mothers and daughters rated overall family functioning (FES), and daughters rated parental relationships (IPPA, MFP). Metabolic control was assessed using HbA1c levels. MANCOVA illustrated that eating disturbances are associated with the perception of poor communication with mothers and fathers, a lack of trust in their accessibility and responsiveness, and overall family environments perceived to be conflictual and inadequate in support and structure. Regression analyses revealed that the presence and severity of an eating disturbance mediates the influence of family functioning on metabolic control.