Hemiplegic migraine (HM), a rare form of migraine with aura, has a female predominance of 2–4:1 with most common onset between 12 and 17 years of age. Hemiplegic migraine can occur sporadically or pass familiarly with autosomal dominant transmission. Those with familial hemiplegic migraine (FHM) are categorized into four groups (FHM1–4) according to the gene mutation they possess. Those designated FHM1 account for approximately 50% of those with FHM and possess mutations in the CACNA1A gene on chromosome 19p13. Those with subgroups FHM2 and FMH3 possess gene mutations in ATP1A2 and SCN1A, respectively. Patients with a family history (at least one affected first-degree or second-degree relative) of HM, however, with no found gene mutation are designated FHM4.