The association between hereditary myotonic disorders and epilepsy is seldom described in the literature. To date, few reports have dealt with dystrophic myotonias, whereas a single case demonstrating an association between sporadic congenital myotonia and epilepsy was recently reported in a patient carrying a de novo mutation of the CLCN1 gene. Additional evidence for a role of CLCN1 in the pathogenesis of epilepsy is derived from large-scale exome analysis of ion channel variants and expression studies. Here, we describe the first case of association between familial Thomsen myotonia and epilepsy. All the affected members of a two-generation family presented myotonia and disclosed a pathogenic mutation in CLCN1. In addition, one individual experienced epileptic seizures due to limbic encephalitis (LE) with anti-GAD antibodies. The occurrence of the two diseases in this patient could be a chance association, however, CLCN1 mutation, as a susceptibility factor for epilepsy through dysfunction of GABAA inhibitory signalling, cannot be ruled out as a possible influence.