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We report a case of a Chinese neonate who was diagnosed with Noonan syndrome and had persistent, self-limited thrombocytopenia. The neonate was admitted to the Neonatology Department 20 minutes after birth because of respiratory distress. From birth until 2 months of age, platelet values fluctuated between approximately 6 and 30 × 10 9 /L. There was no intracranial hemorrhage. However, the child had a transient hypocalcemic seizure and fever. We excluded thrombocytopenia caused by perinatal asphyxia, immune thrombocytopenia, fetomaternal alloimmune thrombocytopenia, juvenile myelomonocytic leukemia, and chromosome 13, 18, and 21 trisomy syndromes. Despite treatment with anti-infective agents and transfusion of platelets and immunoglobulin, the platelet count did not return to the normal range. Genetic testing confirmed a PTPN11 gene mutation, which led to the diagnosis of Noonan syndrome. At 3 months of age, the platelet count gradually increased without intervention and returned to the normal range by 6 months. We speculate that the thrombocytopenia in this case was closely related to Noonan syndrome.