Context: No consensus exists for management of adults with congenital adrenal hyperplasia (CAH) due to a paucity of data from cohorts of meaningful size. Objective: Our objective was to establish the health status of adults with CAH. Design and Setting: We conducted a prospective cross-sectional study of adults with CAH attending specialized endocrine centers across the United Kingdom. Patients: Participants included 203 CAH patients (199 with 21-hydroxylase deficiency): 138 women, 65 men, median age 34 (range 18-69) years. Main Outcome Measures: Anthropometric, metabolic, and subjective health status was evaluated. Anthropometric measurements were compared with Health Survey for England data, and psychometric data were compared with appropriate reference cohorts. Results: Glucocorticoid treatment consisted of hydrocortisone (26%), prednisolone (43%), dexamethasone (19%), or a combination (10%), with reverse circadian administration in 41% of patients. Control of androgens was highly variable with a normal serum androstenedione found in only 36% of patients, whereas 38% had suppressed levels suggesting glucocorticoid overtreatment. In comparison with Health Survey for England participants, CAH patients were significantly shorter and had a higher body mass index, and women with classic CAH had increased diastolic blood pressure. Metabolic abnormalities were common, including obesity (41%), hypercholesterolemia (46%), insulin resistance (29%), osteopenia (40%), and osteoporosis (7%). Subjective health status was significantly impaired and fertility compromised. Conclusions: Currently, a minority of adult United Kingdom CAH patients appear to be under endocrine specialist care. In the patients studied, glucocorticoid replacement was generally non-physiological, and androgen levels were poorly controlled. This was associated with an adverse metabolic profile and impaired fertility and quality of life. Improvements in the clinical management of adults with CAH are required. (J Clin Endocrinol Metab 95: 5110-5121, 2010)