We describe a Swedish family with the proband and his brother suffering from severe Romano-Ward syndome (RWS) associated with compound heterozygosity for two mutations in the KVLQT1 (also known as KCNQ1 and KCNA9) gene (R518X and A525T). The mutations were found to segregate as heterozygotes in the maternal and the paternal lineage, respectively. None of the heterozygotes exhibited clinical long QT syndrome (LQTS). No hearing defects were found in the proband. The data strongly indicates that the compound heterozygosity for R518X and A525T is the cause of an autosomal recessive form of RWS in this family. Our findings support the implication of a higher frequency of gene carriers than previously expected. We suggest that relatives of 'sporadic RWS' patients should be considered potential carriers, at risk of dying suddenly from drug-induced LQTS.