We hypothesized that type 2 diabetes among adolescents occurs within families in which known diabetes risk factors are prevalent. Therefore,we investigated these families in order to define the presence of known risk factors and to determine whether a profile of the at-risk family can be identified. A total of 42 subjects from 11 families with adolescent previously diagnosed with type 2 diabetes participated. All subjects underwent anthropometric measurements, as well as determination of fasting glucose, HbA1c C-peptide, pro-insulin, and insulin. Subjects also completed food frequency and DSMIV eating disorder questionnaires. Results: Forty-five percent of mothers and 36% of fathers had been diagnosed with type 2 diabetes prior to the study. An additional 40% of the fathers were diagnosed with type 2 diabetes as part of their participation. Mothers affected with type 2 diabetes had markedly abnormal hemoglobin A1c values indicating poor control. As a group, participants were obese, with BMI above the 95%ile for probands and fathers, and at the 85%ile for mothers and siblings. The sum of skin folds was above the 95% percentile for the patients, 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 the vast majority reported no regular physical activity. Three (27%) of the probands met the criteria for Binge Eating Disorder and six additional patients had significant characteristics of the disorder. None of the siblings (mean age 14±0.3 yrs) had elevated glucose or HbA1c levels. However, siblings had markedly elevated fasting C-peptide (0.69 ± 0.13 nmol/L vs normal 0.46± 0.03) and proinsulin levels (20.1 ± 5.1 pmol/L vs normal 8.6± 0.64). Previously undiagnosed mothers also displayed signs of insulin resistance, with C-peptide of 0.85 ± 0.12 nmnol/l and proinsulin of 18.8 ± 8.6 pmol/l. CONCLUSIONS: Probands, as well as other family members, are centrally obese and have lifestyles characterized by high fat intake, minimal physical activity and a high incidence of binge eating disorders. Furthermore, the incidence of diagnosed and undiagnosed type 2 diabetes and insulin resistance in these families is striking. Taken together, these findings suggest that adolescent type 2 diabetes frequently occurs in a high-risk family setting and indicate that screening of family members for diabetes may be appropriate. Furthermore, treatment programs for adolescents with type 2 diabetes will need to address the lifestyle and health habits of the entire family.