Fibrous dysplasia of the mandible typically begins during toddler years and culminates during puberty. These lesions may cause jaw disfigurement and may not be amendable to surgery. Imatinib successfully has treated cherubism associated with SH3BP2 mutations, but similar lesions can present in other conditions such as Noonan syndrome. We report diagnosis of Noonan syndrome caused by a PTPN11 activating mutation and successful treatment of the fibrous dysplasia of the mandible with imatinib.