BACKGROUND: Familial cortical myoclonic tremor with epilepsy (FCMTE) is defined by autosomal dominant adult-onset cortical myoclonus (CM) and seizures in 40% of patients. Two loci, 8q23.3-q24.11 (FAME1/FCMTE1) and 2p11.1-q12.2 (FAME2/FCMTE2), were previously reported without an identified gene. Unlinked families argue for a third mutated gene. METHODS: A genome-wide scan was performed in a large FCMTE family using Linkage-12 microarrays (Illumina). Refinement of the locus on 5p was performed by genotyping 13 polymorphic microsatellite markers in the 45 available family members. RESULTS: This large French FCMTE family included 16 affected relatives. The first symptoms were CM in 5 patients (31.2%), seizures in 5 patients (31.2%), and both at the same time in 6 patients (37.5%). A total of 12.5% (2/16) had only CM without seizures. The genome-wide scan identified a single region on 5p15.31-p15, with a multipoint lod score of 3.66. Further genotyping of all family members confirmed that the region spans 9.31 Mb between D5S580 and D5S2096, 2-point lod scores reaching 6.3 at theta = 0 for D5S486. Sequencing of the SEMA5A and CTNND2 genes failed to detect mutations. CONCLUSIONS: We report the clinical and genetic characteristics of a large familial cortical myoclonic tremor with epilepsy family. The third gene maps to 5p15.31-p15. Identification of the mutated gene is ongoing.