Objective: To identify physical, behavioral, and environmental features of adolescents (aged 11-17 years) with type 2 diabetes mellitus and their families to define the involvement of known risk factors and to define a profile of at-risk individuals. Design and Methods: A total of 42 subjects from 11 families with an adolescent in whom type 2 diabetes was previously diagnosed participated. All subjects underwent anthropometric measurement and completed food frequency and eating disorder questionnaires, and were classified according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition. In addition, laboratory tests to determine levels of hemoglobin A(1c), fasting glucose, C peptide, insulin, and proinsulin were performed. Results: Type 2 diabetes had been diagnosed in 5 of 11 mothers and 4 of 11 fathers before the study. Type 2 diabetes was diagnosed in 3 of the remaining 7 fathers during the study. In 3 families, both parents were affected with type 2 diabetes. As a group, participants were obese, with a body mass index higher than the 95th percentile for probands and fathers, and higher than the 85th percentile for mothers and siblings. The sum of skin fold measurements was above the 95th percentile for the probands, their siblings, and the parents. All groups had high fat intake and low fiber intake. None of the subjects participated in a structured or routine exercise program, and most reported no regular physical activity. Three of the probands met the criteria for binge-eating disorder, and 6 additional patients had notable characteristics of the disorder: Mothers affected with type 2 diabetes had markedly abnormal hemoglobin A(1c) levels, indicating poor control. There were no group differences in fasting concentrations of insulin, proinsulin, or C peptide. However, a third of the mothers with type 2 diabetes, and all but 1 of the siblings, had evidence of insulin resistance. Conclusions: Adolescents in whom type 2 diabetes has been diagnosed, as well as their first-degree family members, are obese. In addition, the incidence of diagnosed and undiagnosed type 2 diabetes or of insulin resistance in the families of adolescents with type 2 diabetes is striking. Probands and other family members have lifestyles characterized by high fat intake, minimal physical activity, and a high incidence of binge eating. These findings indicate that the families of adolescents with type 2 diabetes share many anthropometric and lifestyle risk factors. The design of treatment programs for adolescents with type 2 diabetes will need to address the lifestyle and health habits of the entire family.