AIM To determine the clinical and biological characteristics of double diabetes(DD) among young people in Saudi Arabia.METHODS This was a retrospective descriptive chart review study including 312 young newly diagnosed diabetic patients(aged 12-20 years), whom were admitted over a five year period(January 2009 to December 2013). Family history of diabetes mellitus(DM)(first degree), physical body mass index(BMI), acanthosis nigricans, history of auto-immune disease and laboratory information for glycosylated hemoglobin, basal C peptide level and diabetes autoantibody response(anti-GAD, anti-IA2 and anti-ICA) were collected from medical report. A mean follow-up of 3 years for these patients was performed.RESULTS Patients were categorized into 4 groups, based on the autoantibody response(Ab+ or Ab-) and C-peptide secretion(β+ for fasting level 0.4-2.1 ng/mL and β- if < 0.4 ng/mL). Group1(type 1a): Ab+ β-(21%), group 2(type 1b): Ab- β-(9%), group 3(DD): Ab+ β+(31%)and group 4(classic type 2 DM): Ab- β+(39%). The mean age of the DD patients in our study was 15.1 ± 6.4 years. A total of 41% of the study population presented with diabetic ketoacidosis and 61% of the study population presented with positive family history of DM. The mean BMI was 26.8 kg/m2 with 64% of overweight or obese patients. Ninety two percent of the patients were started on insulin at the time of diagnosis. During a mean follow-up of 3 years, only 32% of the patients with DD required insulin and 78% were on metformin alone or with insulin. CONCLUSION Our findings enable us to arrive at the conclusion that almost one-third of the young Saudi diabetic patients reveal atypical forms of DM(double diabetes) expressing features resulting from both T1D and T2D. AIM To determine the clinical and biological characteristics of double diabetes (DD) among young people in Saudi Arabia. METHODS This was a retrospective descriptive chart review study including 312 young newly diagnosed diabetic patients (aged 12-20 years), whom were admitted over a Family history of diabetes mellitus (DM) (first degree), physical body mass index (BMI), acanthosis nigricans, history of auto-immune disease and laboratory information for glycosylated hemoglobin, basal C peptide level and diabetes autoantibody response (anti-GAD, anti-IA2 and anti-ICA) were collected from medical report. A mean follow-up of 3 years for these patients was performed. Group1 (type 1a): Ab + - (21%), Ab1 + (Abeta or Ab-) and C-peptide secretion group 2 (type 1b): Ab- β- (9%), group 3 (DD): Ab + β + (31%) and group 4 type 2 DM): Ab- beta + (39%). The mean age of the DD patients in our study was 15.1 ± 6.4 years. A total of 41% of the study population presented with diabetic ketoacidosis and 61% of the study population The mean BMI was 26.8 kg / m2 with 64% of overweight or obese patients. Ninety two percent of the patients were started on insulin at the time of diagnosis. During a mean follow-up of 3 years , 32% of the patients with DD required insulin and 78% were on metformin alone or with insulin. CONCLUSION Our findings enable us to arrive at the conclusion that almost one-third of the young Saudi diabetic patients reveal atypical forms of DM (double diabetes) expressing features from both T1D and T2D.