We describe the Leuven experience with 52 males with Aarskog syndrome particularly with respect to clinical variability, changing phenotype with age, and previously unreported signs. At least 30% of affected males were mentally retarded, two thirds of them at the level of slight mental handicap. Hyperactive behavior and symptoms of attention deficit disorders were frequently observed (61% of the mentally normal and 84% of the mentally subnormal), but regressed completely after the age of 12 to 14 years. The social integration and functioning as adults is satisfactory. Postpubertal males with Aarskog syndrome have only minor remnant manifestations of the prepubertal phenotype, making clinical diagnosis in adults extremely difficult.