Mutations involving the voltage-gated sodium channel a I gene SCN1A are major genetic causes of childhood epileptic disorders, as typified by Dravet syndrome. Here we investigated the upstream regions of the SCN1A 5 0 noncoding exons and found two major regions with promoter activity. These two major promoters were simultaneously active in various brain regions and in most neurons. Using multiplex ligation-dependent probe amplification (MLPA) assays with probes for the 5 0 noncoding exons, their upstream regions, and all coding exons of SCN1A, we investigated 130 epileptic patients who did not show any SCN1A mutations by sequence analysis of all coding exons and exon-intron boundaries. Among 71 Dravet syndrome patients, we found two patients with heterozygous microdeletions removing the 5 0 noncoding exons and regions with promoter activity but not affecting the coding exons. We also identified four patients with deletions/duplication in the coding region. One patient with symptomatic focal epilepsy also showed a deletion in the coding region. This study provides the first case of microdeletion limited to the SCN1A 5 0 promoter region with the coding sequence preserved, and indicates the critical involvement of this upstream region in the molecular pathology of Dravet syndrome.