ABSTRACT Hereditary lymphedema type I (Milroy disease) is a rare autosomal dominant disease resulting from mutations of FLT4 encoding the vascular endothelial growth factor receptor-3. Patients develop edema of the legs and feet, resulting in chronic swelling of the lower extremities from the neonatal period. Here we report a Japanese family with 10 affected members of five generations of hereditary lymphedema type I. We identified a previously reported missense mutation of G857R in one allele of FLT4 from three affected individuals of three generations, the mother of whom presented only hemi-lymphedema of the left foot. Thus, the clinical features of hereditary lymphedema type I caused by a FLT4 mutation are heterogeneous and it would be appropriate to consider FLT4 mutations even in a patient with hemi-lymphedema of the foot.