McLeod syndrome is a rare X-linked hematologic and neuromuscular disorder manifested by chorea, myopathy, cardiomyopathy, areflexia, hyperCKemia, and acanthocytosis. Only four mutations have been reported in the gene responsible for McLeod syndrome. We report a novel gene mutation in a Japanese family. Direct sequencing of the PCR-amplified genomic DNA revealed the mutation was a single C-nucleotide insertion at codon 151 in exon 2 of the XK gene, which resulted in a 3'-frameshift. Study of family members revealed that the patient's mother was a manifesting carrier heterozygous for this mutation.