The prevalence of type 1 (T1DM) and type 2 diabetes mellitus (T2DM) in youth is on the rise. The increased incidence of obesity makes classifying diabetes difficult. At diagnosis, most young people present with characteristics of either T1DM or T2DM. Young people with double diabetes are obese, insulin resistant and have the immunological markers of T1DM. The appropriate markers must be used to identify double diabetes. Complications of double diabetes include abnormal lipids, polycystic ovary syndrome, hypertension, vitamin D inadequacy, and increased cardiovascular risk. Medical nutrition therapy is vital to the treatment and prevention of double diabetes and its complications.A PPROXIMATELY 1 in 400 children and adolescents younger than 20 years has diabetes, categorizing diabetes as the third most common chronic disease in childhood. 1,2 The prevalence of both type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) is on the rise. According to the EURODIAB (a collaborative European study of issues around diabetes) group, the incidence of T1DM has increased by 3.2% annually over the past several decades; especially in children younger than 5 years. 3 This increase has suggested a relationship to environmental changes rather than genetic, due to the short period of time of increased incidence. Furthermore, the multicenter, population-based SEARCH, a multicenter study to understand more about diabetes in young adults and children that is conducted in the United States, determined the incidence of T1DM in Colorado youth increased by 2.7% per year in the non-Hispanic white population and 1.6% per year in Hispanic youth. 4 The largest increase was seen in children aged 0 to 4 years (3.5% per year), similar to the European data.The incidence of T2DM in the pediatric population has increased 10-fold over the past 10 years resulting in 3700 new cases per year related to obesity and sedentary lifestyle. 5 It is projected that more than 30% of children born in the year 2000 will develop diabetes during their lifetime. 3 This high rate of T2DM is mainly seen in adolescents aged 15 to 19 years in minority populations. 6 Despite the rise in both types of diabetes, classifying T1DM and T2DM in the pediatric population is not straightforward. Research