Germline mutations in PTPN11--the gene encoding the nonreceptor protein tyrosine phosphatase SHP-2--represent a major cause of Noonan syndrome (NS), a developmental disorder characterized by short stature and facial dysmorphism, as well as skeletal, hematologic, and congenital heart defects. Like many autosomal dominant disorders, a significant percentage of NS cases appear to arise from de novo mutations. Here, we investigated the parental origin of de novo PTPN11 lesions and explored the effect of paternal age in NS. By analyzing intronic portions that flank the exonic PTPN11 lesions in 49 sporadic NS cases, we traced the parental origin of mutations in 14 families. Our results showed that all mutations were inherited from the father, despite the fact that no substitution affected a CpG dinucleotide. We also report that advanced paternal age was observed among cohorts of sporadic NS cases with and without PTPN11 mutations and that a significant sex-ratio bias favoring transmission to males was present in subjects with sporadic NS caused by PTPN11 mutations, as well as in families inheriting the disorder.