There are no studies that compare the prevalence of organ-specific autoantibodies (OSAs) between adult (≥ 16 years) and childhood-onset type 1 diabetes (T1D). We evaluated the prevalence of the following OSAs: thyroid peroxidase, thyroid receptor, parietal cell, intrinsic factor, tissue transglutaminase, adrenal cortex, mitochondrial, smooth muscle, liver kidney microsomal, and ovarian autoantibodies. Three hundred twenty-seven (327) adults were screened for one or more of these OSAs. The prevalence of all the OSAs studied was similar in both groups. The most prevalent OSA observed was tissue transglutaminase (childhood-onset disease = 14.3%; adult-onset disease = 13.6%). This study did not demonstrate a distinct difference in the prevalence of OSAs between adult- and childhood-onset T1D patients.