Primary adrenocortical insufficiency (Addison's disease) is a potentially fatal condition that often develops insidiously and can be easily overlooked. Although rare in the general population, it is more common in patients with type 1 diabetes mellitus (T1DM). The combination of Addison's disease with T1DM and/or autoimmune thyroid disease is known as autoimmune polyendocrine syndrome type-2 (APS-2). T1DM commonly precedes the development of adrenocortical insufficiency in most patients with APS-2. We, in this study, present four cases of Addison's disease developing in adolescents with pre-existing T1DM. Risk factors for Addison's disease in this population include a history of other organ-specific autoimmunity, particularly thyroid, and a positive family history. In addition to the 'classic' Addisonian features, the development of unexplained recurrent hypoglycemia, reduction in total insulin requirement, improvement in glycemic control, or abnormal pigmentation should arouse suspicion of adrenocortical insufficiency. Adrenal antibodies have been proposed as a screening tool for Addison's disease in the T1DM population, but doubts remain about their specificity and sensitivity. The addition of specific HLA DRB1 subtyping has been proposed to improve predictive value.