We developed a 4-session, multifamily group therapy program for older children and adolescents with insulin-dependent diabetes mellitus (IDDM) and their caregivers, based on the problem-solving and communication skill components of Behavioral Family Systems Therapy for Diabetes (BFST-D; Wysocki et al., 2006). The central goal of this study was to use a retrospective chart review design to assess changes in youths' glycosylated hemoglobin (HbA1c) associated with group participation as part of routine clinical care. Participants were 67 children and adolescents with Type 1 diabetes or insulin-dependent Type 2 diabetes (M = 14.22 years, 58% female) who were experiencing poor glycemic control and/or adherence challenges. After controlling for child age and diabetes duration, the interaction of pretreatment HbA1c and binary session attendance (1 or 2 sessions vs. 3 or 4 sessions) significantly predicted posttreatment HbA1c and likelihood of improvement in HbA1c by at least 0.5%. Post hoc probing indicated that—among youth with higher pretreatment HbA1c—attending at least 3 sessions was associated with significantly lower HbA1c at posttreatment. To assess treatment acceptability to families, patient satisfaction data also were examined for a subset of patients and indicated that both parents and youths were satisfied with the intervention. Findings suggest that this multifamily group problem-solving program is an acceptable and promising intervention for youth with IDDM experiencing diabetes management challenges.