To investigate chloride channel 1 (CLCN1) gene mutation and clinical features of 2 Chinese patients with myotonia congenita.Clinical data of a patient from a family affected with myotonia congenita in addition with a sporadic patient from Fujian province were analyzed. Exons of CLCN1 gene were amplified and sequenced.The proband from the affected family was found to carry a c.1024G>A heterozygous missense mutation in exon 8, whilst the sporadic patient has carried a c.1292C>T heterozygous missense mutation in exon 11.Detection of CLCN1 gene mutation is an effective method for the diagnosis of myotonia congenita. Exon 8 of CLCN1 gene may be a mutational hotspot in Chinese patients with myotonia congenita.