Objective The aim of the study was to explore the clinicopathologic, immunophenotypic, and diagnostic features of extramedullary metastases of glioblastoma. Methods One case of extramedullary skeletal muscle metastasis of glioblastoma was studied, including the clinical, histological, and immunohistochemical features. Results A 24-year-old man underwent surgical resection for glioblastoma(WHO grade IV) in the left temporal parietal region followed by radiotherapy and temozolomide therapy. One year and nine months later, he developed an extramedullary skeletal muscle metastasis in L4, and the histology was remarkably different from that of the primary glioblastoma specimen. The immunohistochemical analysis also showed changes. In the metastasis, the small cells were negative for GFAP; weakly positive for S-100; and positive for nestin, NSE, and CD56, with 60% of cells positive for p53 and 40% positive for Ki-67. The giant cells showed strong positivity for GFAP and S-100, and weak expression of p53, Ki-67, nestin, NSE, and CD56. The primary glioblastoma specimen showed strong positivity for GFAP and S-100 and was negative for NSE, nestin, and CD56, with around 25% of the tumor cells positive for p53 and a Ki-67 labeling index of 20%. Conclusion Extraneural metastasis(ENM) is a rare complication of glial tumors and glioma stem cells may be related to the metastasis. Since extraneural metastasis may occur in patients without central nervous symptoms, any unusual signs during the follow-up of patients diagnosed with glioblastoma should not be underestimated. Objective The aim of the study was to explore the clinicopathologic, immunophenotypic, and diagnostic features of extramedullary metastases of glioblastoma. Methods One case of extramedullary skeletal muscle metastasis of glioblastoma was studied, including the clinical, histological, and immunohistochemical features. Results A 24- year-old man underwent surgical resection for glioblastoma (WHO grade IV) in the left temporal parietal region followed by radiotherapy and temozolomide therapy. One year and nine months later, he developed an extramedullary skeletal muscle metastasis in L4, and the histology was remarkably different from the of the primary glioblastoma specimen. The immunohistochemical analysis also showed changes. In the metastasis, the small cells were negative for GFAP; weakly positive for S-100; and positive for nestin, NSE, and CD56, with 60% of cells positive for p53 and 40% positive for Ki-67. The giant cells showed strong positivity for GFAP and S-100, and weak expre ssion of p53, Ki-67, nestin, NSE, and CD56. The primary glioblastoma specimen showed strong positivity for GFAP and S-100 and was negative for NSE, nestin, and CD56, with around 25% of the tumor cells positive for p53 and a Ki-67 labeling index of 20%. Conclusion Extra-renal metastasis (ENM) is a rare complication of glial tumors and glioma stem cells may be related to the metastasis. Since extraneural metastasis may occur in patients without central nervous symptoms, any unusual signs during the follow-up of patients diagnosed with glioblastoma should not be underestimated