Background: Type 1 Diabetes mellitus (T1DM) results from a cellular-mediated autoimmune destruction of the β-cells of the pancreas. We designed this study to determine the prevalence of autoantibodies among Saudis patients with T1DM. Methods: Glutamic acid decarboxylase antibodies (GADA), antibodies to Islet cell (ICA) and Insulin (IAA) were measured in 171 Saudis patients with T1DM. Results: There were 171 patients with T1DM, 71 males (41.5%) and 100 females (58.5%). The mean age was 20.8 ± 6.6 and the mean diabetes duration was 7.7 ± 5.7. GADA, ICA and IAA were detected in 53.8%, 32.2% and 76% respectively. GADA, ICA and IAA were nonsignificantly more frequent in female and GADA and IAA were significantly more frequent in those younger than 20 years of age. Subjects testing positive for GADA had higher levels of ICA (42.4% vs. 20.3, p = 0.003) and IAA (79.3% vs. 72.2, p = 0.3) than those negative for GADA. Multiple antibodies (≥2) were observed more often in patients under the age of 20 years. There were nonsignificant differences in the prevalence of multiple antibodies between both genders. Multiple logistic regression analysis showed a significant independent positive relationship between the serum positivity of GADA, ICA and Multiple antibodies (≥2) with diabetes duration (0.02, p = 0.03, 0.02, p = 0.01 and 0.01, p = 0.04 respectively). Conclusions: The prevalence of autoantibodies in Saudi patients with T1DM is similar to those reported for diabetic patients in other ethnic groups.