Background: Adrenal hypoplasia congenita (AHC) is a rare disease (1:70.000 men) characterized by reduction in all cortical adrenal hormones and also by hypogonadism. NR0B1 -related AHC includes both X-linked AHC and Xp21 deletion. AHC gene mutation was first described in 1994 and occurs in less than 1% of adrenal insufficiency (AI) cases and it is imperative that clinical endocrinologists increase their knowledge on this condition to recognize it as promptly as they were used to do so in other causes of pediatric AI.Clinical Cases: We describe here two sporadic cases and three familial cases from one family, all of them attending at our Endocrine Unit at HCPA, in the South of Brazil. The median age of AI first symptoms was 1 month old in two patients (acute infantile onset due to a salt wasting crises), and eleven years old in the remaining patients (childhood onset). Their exams confirmed the clinical suspicion of primary AI because of low plasma cortisol (from < 0.5 to 4 mcg/dl - reference range from 7-24 mcg/dl), as well as all adrenal steroids levels, high ACTH levels (from 672 to 2225 pg/ml - reference range from 7-63 pg/ml) and high plasmatic renin (from 92 to 448 mcUI/ml - reference range from 2.8-39.9 mcUI/ml). They were also extensively investigated searching for the AI pathophysiology. After some years of lost follow-up, one of the familial cases that had first been seen in 1993, returned to our hospital and was diagnosed with hypogonadism, leading to NR5OB1 gene evaluation.Regarding the genetic etiology, one of the sporadic cases developed a clinical picture including profound developmental delay, seizures and strabismus suggestive of a contiguous gene syndrome that involves Duchenne muscular dystrophy, glycerol kinase deficiency and AHC. A CGH array was performed and identified a Xp21.3-p21.1 deletion. The affected family had an extensive history suggestive of a genetic disease with X-linked inheritance pattern, as shown by the premature death of 3 uncles and a male cousin. A deleterious variant (c.131_212delinsTGAGACCTGTACCGT) in NR5OB1 gene was identified by Sanger sequencing in hemizygous state in the 46,XY affected patients.Conclusion: Albeit a rare disease, it is crucial that endocrinologist all around the World could be aware about clinical characteristics of this condition in order to properly diagnose it. And it is even possible, as it occurred with one of our patient, to make a late pathophysiologic diagnosis, making possible to treat the associated hypogonadism. Reference: Acherman JC, Vilain EJ. NR0B1- related adrenal hypoplasia congenita. GeneReviews 1993-2019.