Herein, we report two girls with a neonatal screening (NS)-negative 21-hydroxylase deficiency (21-OHD) requiring treatment with hydrocortisone due to virilization that developed in late childhood. Patient 1 was born prematurely on the 30th gestational week with normal external genitalia at birth. She passed the NS for 21-OHD. At 6 yr of age, she was referred to a hospital for evaluation of premature pubarche and clitoromegaly. Her diagnosis was central precocious puberty, and GnRH agonist was initiated. However, her symptoms did not improve despite treatment for over 4 years. She was then referred to our hospital where she was diagnosed with 21-OHD. Although she was started on hydrocortisone therapy, her adult height reached only 140 cm (-3.4 SD). Patient 2 was delivered at 37 weeks of gestation and passed the NS for 21-OHD. She was referred to a hospital because of premature pubarche at the age of 6 yr. She was diagnosed with 21-OHD, and hydrocortisone replacement therapy was initiated. Her present height at 13 yr of age is 148 cm (-1.3 SD). These cases reminded us that the possibility of 21-OHD should be considered when patients show premature pubarche or precocious puberty, even if they passed the NS test for 21-OHD.