No association of familial adenomatous polyposis (FAP) and hereditary spherocytosis (HS) has been reported, both of which are inherited in an autosomal dominant manner. We present the first reported case of FAP with spherocytosis and construct the family pedigree. In the patient's pedigree, both FAP and spherocytosis were inherited in an autosomal dominant trait. In the 34-year-old Japanese proband's leukocytes, we found no abnormal chromosomal band, and a germline mutation of the APC gene was not detected. All possible genes reported to be linked to HS were located far from chromosome 5q on which the APC gene is located. Although it is unknown if erythrocyte membrane disorder is an additional phenotype of FAP, to the best of our knowledge, this is the first documentation of FAP associated with spherocytosis.