We reviewed retrospectively 12 muscle biopsies of patients who were clinically diagnosed with a primary muscle diseases from the clinical data base of Thammasat University Hospital from January 2005 to January 2007. Most patients were male and had median age of 30.5 years (range 14 to 56). The most common clinical presentation was proximal muscle weakness. Nine of eleven patients had elevated CK concentrations ranging from 338 to 1,023 IU/L. Clinicopathological correlation revealed specific diagnoses in nine patients. Suspected cases of mitochondrial neurogastrointestinal encephalopathy (MNGIE), myofibrillar myopathy (MFM) and distal myopathy with rimmed vacuoles (DMRV) were confirmed by molecular genetic studies examing thymidine phosphorylase, GNE, ZASP, myotilin, desmin, aβ-crystalline and filamin C genes. Specific histopathological findings on muscle biopsy help to select cases for advance molecular testing.