Familial hemiplegic migraine is a hereditary form of migraine in which the aura includes a certain degree of motor deficit. A first gene responsible for this disease was located on chromosome 19 in 1993, and identified in 1996. It encodes the principal alpha 1-subunit of a potential-dependent calcium channel, the P/Q channel, which is selectively expressed in the nervous system. This channel is particularly rich in nerve terminals, where it contributes to the triggering and release of neuromediators. In patients with hemiplegic migraine, mis-sense mutations have been detected which result in a modification of channel function. Other mutations which lead to the synthesis of inactive protein truncations have been described in another disease, type 2 episodic ataxia. In the mouse, mutations in the same gene lead to different phenotypes (tottering mouse, leaner mouse). Finally, possible links between P/Q calcium channel dysfunction and migraine have been discussed.