We studied mutations of the ankyrin-1 (ANK-1) gene of genomic DNA from Japanese patients with hereditary spherocytosis (HS). Forty-nine patients from 46 unrelated families were included in this study. Of these patients, 19 cases from 16 unrelated families had HS of autosomal-dominant inheritance, and 30 patients had non-autosomal-dominant HS. Fifteen mutations of the ANK-1 gene pathognomonic for HS were identified: 4 nonsense mutations, 7 frameshift mutations, and 4 abnormal splicing mutations. These 15 mutations have not been previously reported. The frameshift mutations were found from exon 1 to exon 26, corresponding particularly to the band 3-binding domain of ankyrin. The nonsense mutations, on the contrary, were present mostly at the 3'-terminal side, especially in the spectrin-binding domain and the regulatory domain. The patients with ankyrin gene mutations tended to be more anemic with a higher level of reticulocytosis than those without these mutations. Fifteen silent mutations of the ANK-1 gene, most of which have previously been detected in HS patients in Western populations, were also found. The allele frequency of these silent mutations in the HS patients was nearly identical to that in normal subjects. There was no difference between the Japanese and Western populations in the allele frequency of these gene polymorphisms in healthy subjects or HS patients.