Infantile hypertrophic pyloric stenosis (IHPS) is a common surgical condition of unknown etiology. The oral mucosal vascular networks of IHPS patients (n=25) and their unaffected parents showed lower blood vessel-free areas, as well as higher box-counting dimensions at two box size scales [D(1–46), D(1–15)], and relative Lempel-Ziv values (P<0.000001), as compared to those of gender- and age-matched controls. These findings may provide a useful phenotypical marker for identifying couples potentially at risk for the birth of an affected infant, while supporting the importance of a genetic component in this condition.