A case of familial paroxysmal dystonic choreoathetosis (PDC) documente
d by video/EEG monitoring is described. The father of the proband is a
ffected by exertional cramping but not PDC, lending support to the pre
vious hypothesis that exertional cramping may represent a ''forme frus
te'' or the incomplete expression of PDC. Other family members affecte
d by PDC are women, with exercise-induced cramping alone found in two
men. Two of the women report prolonged exertion as a precipitant of le
ngthy spells consistent with typical PDC rather than the previously de
scribed ''intermediate,'' exercise-induced form of PDC. Exertional cra
mping in families affected by PDC may represent the variable expressio
n of the ''dystonia gene'' in male members. Conversely, exercise-induc
ed PDC, both of the intermediate and longer form described here, may h
ave a predilection to manifest in women.