To elucidate the etiology of chorea, we performed gene diagnoses of 79 consecutive cases of the disease (34 males, 45 females; age 15-79 years), which include 39 familial cases (37 pedigrees) and 40 sporadic cases, from 1997 to 2002, after their informed consent was obtained. We extracted genomic DNA from peripheral white blood cells, and performed genetic tests for Huntington disease (HD), dentatorubral pallidoluysian atrophy (DRPLA), Huntington disease like 1 (HDL1), HDL2 and spinocerebellar ataxia type 17 (SCA17). We found 37 cases (36 pedigrees) of HD, seven cases (seven pedigrees) of DRPLA. No cases of HDL1, HDL2 and SCA17 were found. We also found three cases (two pedigrees) presenting an autosomal dominant trait with an unknown origin, and two cases whose parents were consanguineously related. Therefore, further genetic heterogeneity is expected in the cases of chorea in Japan.