Primary adrenal insufficiency (PAI) in the pediatric population (0-18 yr) is most commonly attributed to congenital adrenal hyperplasia (CAH), which occurs in about 1 in 15,000 births, followed by Addison's disease, with an assumed autoimmune etiology. However, molecular advances have increased the number of possible diagnoses. The objective of this study was to determine the incidence and etiologies of PAI in our pediatric population. All patients with a diagnosis of PAI followed by the Endocrinology Service at our institution between September 1981 and September 2001 were studied. One hundred three patients (48 boys) were identified, primarily by the Endocrinology Clinic case registry. CAH was the most frequent etiology (71.8%). However, non-CAH etiologies accounted for 28.2%, of which 55% were nonautoimmune in etiology. Importantly, the CAH sex ratio was 1:1, despite the absence of biochemical screening for this condition in Quebec newborns. Patients with autoimmune polyendocrinopathy-candidiasis-ectodermal dysplasia (APECED) developed adrenal insufficiency 4 yr earlier than those with non-autoimmune disease. Finally, we review the rare etiologies of PAI and propose an algorithm to aid in targeted genetic testing.