An androgen receptor (AR) variant (E653K) was found in two unrelated Swedish families. One family had two girls affected with congenital adrenal hyperplasia (CAH) due to steroid 21-hydroxylase deficiency. The girls, who showed mild virilization in relation to their CYP21 genotype, had inherited the AR gene mutation from their father, who showed no symptoms of androgen insensitivity. The other family had a boy with partial androgen insensitivity and ambiguous genitalia, and he had inherited the AR gene mutation from his mother. The mutant receptor showed a transactivating capacity in the same range as the normal receptor at high concentrations of ligand (1 and 10 nM dihydrotestosterone), but absent or reduced transactivation at low levels (0.01 and 0.1 nM). The receptor variant was not found among 250 additional unselected Swedish men. Sequencing of the AR gene in five unrelated CAH girls with the I172N mutation in CYP21 and minimal virilization did not reveal any additional deviations from the normal reference sequence. In addition, there was no difference in lengths of the polymorphic CAG repeat in the AR gene between CAH girls with the I172N mutation who showed minimal and severe virilization, and we found no evidence of skewed X-inactivation. We conclude that AR gene mutations or polymorphisms are not a common factor influencing the degree of hyperandrogenic symptoms displayed by CAH girls, and that the AR E653K mutation is compatible with normal genital development, although it can cause genital malformations in susceptible individuals.