A double-blind, crossover study of a 10 mg folic acid per day (vs. placebo) treatment was carried out in 25 fra(X) males (ages 1-31 years). Each treatment period lasted 6 months. Before, during and after the study, the patients were assessed blindly with psychological, language and behavioral evaluations, and parent or caretaker reports were collected. Standardized testing did not show statistically significant changes in the group as a whole; psychological testing demonstrated a statistically significant improvement on folic acid in the prepubertal males. After uncoding, caretaker or parent reports also demonstrated behavioral improvements in the prepubertal males while being treated with folic acid.