ABSTRACT
Background: Klinefelter syndrome may present as precocious puberty, which can be either central precocious puberty or peripheral precocious puberty, caused by an extragonadal germ cell tumor. Objective: Report two cases of Klinefelter syndrome that presented with precocious puberty due to a ?-hCG producing mediastinal tumor. Method: Review of the clinical history, physical examination, and laboratory investigations. Results: Pseudo-precocity developed some years before diagnosis of -hCG producing tumor. The patients did not have typical physical features of this syndrome. The testes were small and had loose consistency. Conclusion: Klinefelter syndrome must be excluded in all boys presenting with precocious puberty due to a ?-hCG producing tumor. Conversely, patients with Klinefelter syndrome should be regularly checked for ?-hCG and ?-fetoprotein levels. In those cases, the patients can be diagnosed and treated early. With the early treatment, they will be able to attain normal adult height and have fewer complications from the tumor.