Glucocorticoids are essential in the treatment of patients with congenital adrenal hyperplasia (CAH). The opposite actions of glucocorticoids and androgens in bone mass achievement justify a study of bone mineral density (BMD) in these patients. We evaluated BMD in patients with CAH due to classic 21-hydroxylase (CYP21A2) deficiency and investigated the involvement of clinical and laboratory factors in the BMD. This study assessed the clinical and laboratory factors involved in BMD of 45 patients at the Pediatric Unit of Endocrinology, UNICAMP, who had been diagnosed as having classical CAH due to CYP21A2 deficiency including molecular characterization. The sample consisted of 28 females and 17 males; 23 salt-wasting (SW) and 22 simple virilizing (SV) cases, with average of 9.9 years (ranges, 5.1-16.3 years) when bone densitometry was performed. The DEXA method was used for calculating the areal BMD Z score in L2-L4. The variables were analyzed with reference to the BMD for chronological age (BMD/CA), height age (BMD/HA), and bone age (BMD/BA). The mean Z score for BMD/CA was 0.08 +/- 1.21 (-2.55 to 2.64); it was 0.29 +/- 1.33 (-2.01 to 4.00) for BMD/HA, and -0.90 +/- 1.24 (-3.41 to 1.92) for BMD/BA. The BMD/CA was significantly lower in females and in patients on treatment for a long period and of more advanced chronological age. Weight and body mass index (BMI) Z scores showed a positive correlation with advanced BA. The higher the weight and BMI Z scores, the higher the BMD/HA. The BMD/BA values were significantly higher in the group in which BA was closer to CA. The BMD/BA value was significantly lower when compared to the value obtained with height and chronological ages. Sex, duration of treatment, weight, BMI, and bone age have an effect on areal BMD in patients with CAH due to CYP21A2 deficiency, which may be underestimated when evaluated in relation to CA and HA.