Arimidex in McCune Albright Syndrome

Inclusion Criteria: * informed written consent of parent/legal guardian and subject assent (as needed by local requirements) * females less than or equal to 10 years of age * diagnosed with McCune-Albright Syndrome * have progressive precocious puberty Exclusion Criteria: Any one of the following is regarded as a criterion for exclusion from the study: * any prior treatment of MAS associated with progressive precocious puberty with a third generation aromatase inhibitor (anastrozole, letrozole, exemestane) in which no clinical response was seen * concomitant treatment of precocious puberty associated with MAS, with the exception of bisphosphonates for polyostotic fibrous dysplasia and LHRH analogues in the case of central precocious puberty * liver function tests at screening visit (AST, ALT) \> or = 3x the upper limit of the reference range for age * known hypersensitivity to any component of study medication