Objective: Our aim was to determine whether the clinical features of 21-hydroxylase–deficient nonclassic adrenal hyperplasia are correlated with either age at symptom onset or age at presentation, or both, and with the degree of adrenocortical abnormality. Study Design: In a multicenter cohort design 220 women with nonclassic adrenal hyperplasia, with a basal or adrenocorticotropic hormone–stimulated 17-hydroxyprogesterone level >30.3 nmol/L, were studied, either prospectively (n = 39) or retrospectively (n = 181). Patients were stratified by age of presentation into 5 groups: (1) <10 years (n = 25), (2) 10 to 19 years (n = 64), (3) 20 to 29 years (n = 83), (4) 30 to 39 years (n = 30), and (5) 40 to 49 years (n = 16). Two patients >50 years old were excluded from the analysis because of age. Results: Ninety-two percent of patients <10 years old had premature pubarche at presentation, whereas clitoromegaly and acne were each present in only 20% of these younger subjects. With only patients ≥10 years old considered, presenting clinical features included hirsutism (59%), oligomenorrhea (54%), acne (33%), infertility (13%), clitoromegaly (10%), alopecia (8%), primary amenorrhea (4%), and premature pubarche (4%). Among the patients ≥10 years old, the prevalence but not the degree of hirsutism increased significantly with age. Basal levels of 17-hydroxyprogesterone in adolescents were significantly higher than the levels found either in children (<10 years old) or women 40 to 49 years old (P < .01 and P < .03, respectively), although no difference was noted in the stimulated 17-hydroxyprogesterone levels between age groups. The adrenocorticotropic hormone–stimulated levels but not the basal levels of 17-hydroxyprogesterone were significantly higher in patients with clitoromegaly than in women without clitoromegaly. Alternatively, there were no differences in either basal or stimulated 17-hydroxyprogesterone levels between patients with and those without hirsutism, acne, or alopecia. Conclusion: In children <10 years old the most common presenting complaint was premature pubarche, whereas hirsutism and oligomenorrhea were more common in older patients. The prevalence of hirsutism increased with age, suggesting the progressive nature of nonclassic adrenal hyperplasia. Furthermore, the adrenocorticotropic hormone–stimulated levels of 17-hydroxyprogesterone were higher in patients with clitoromegaly, which suggests that the degree of adrenocortical dysfunction in nonclassic adrenal hyperplasia determines, at least in part, the clinical presentation. (Am J Obstet Gynecol 2000;183:1468-74.)