Testolactone is used to treat conditions with excessive estrogen synthesis, e.g. gonadotropin-independent precocious puberty in McCune-Albright syndrome (MAS). Unfortunately, daily treatment with testolactone requires 3 to 4 doses (10-20 tablets) and even at these doses it is sometimes ineffective. We treated a patient with MAS (café-au-lait spots; thelarche at age 2- 6/12 yr; menarche at 5- 5/12 yr; accelerated bone age [BA 10 yr]) with the highly selective aromatase inhibitor anastrozole (1 mg once per day). Tamoxifen 1 mg/kg per day was added for 1 year but was discontinued when an ovarian cyst developed with markedly elevated estradiol levels. Estradiol levels returned to normal after resuming anastrozole-only treatment and accelerated BA progressed only 6 months during 2 1/2 years of treatment. The potent estrogen suppressive action and simple dosage regimen of anastrozole suggest it may be advantageous compared to other aromatase inhibitors such as testolactone or anti-estrogens.