OBJECTIVE Congenital adrenal hyperplasia (CAH) is one of the most prevalent, and potentially severe, genetic inborn errors of steroid synthesis directly affecting metabolism. Most patients are diagnosed and treated at an early age. There have been very limited reports of adults with CAH-associated adrenal myelolipomas. We aimed to analyze two families with CAH-associated giant adrenal myelolipomas caused by defects in CYP21A2 and CYP17A1 genes. METHODS A total of 14 individuals from two unrelated families were identified with either CYP21A2 or CYP17A1 mutations. Of note, 5 patients were found with adrenal myelolipomas. Total DNA isolated from the peripheral blood of the two probands was screened for potential mutations in the following susceptibility genes of CAH: CYP21A2, CYP11B1, CYP17A1, HSD17B3, HSD3B2, ARMC5, and STAR using Target Capture-Based Deep Sequencing; and Sanger sequencing was conducted for the family members to detect the potential mutations. RESULTS In family 1, molecular genetics sequencing revealed a compound heterozygous mutation (c.293-13C>G / c.518T>A, p.I173N) in CYP12A2 in the patient and his brother. In family 2, all three female patients with adrenal myelolipomas were found to have a compound heterozygous mutation (c.1118A>T, p.H373L / c.1459_1467del9, p.D487_F489del) in CYP17A1. CONCLUSIONS To avoid giant CAH-associated adrenal myelolipomas in adults, it is important to identify CAH early so appropriate treatment can be initiated to interrupt the chronic adrenal hyperstimulation resulting from increased ACTH. Genetic testing and counseling could be useful in CAH.