Ion channels regulate the transfer of ions between the outer and the inner surface of the cell membrane. The opening of ion channels may be triggered by the binding of a ligand or variations in the membrane potential. Voltage-gated ion channels are an important class of such channels, that are involved in the generation and propagation of action potentials and play a key role in cell to cell communication. As a consequence of cloning and sequencing of ion channel genes, their role in diseases affecting excitable tissues such as the nervous system, heart and skeletal muscle has been examined, and a new class of diseases has emerged. We will review disorders caused by mutations in voltage-gated ion channels affecting these excitable tissues as well as non-excitable tissues such as the kidney. The clinician should be aware of this new class of diseases because pharmacological agents modulating channel functions are available. Characterization of these gene defects should lead to better treatment of these disorders.