This paper shows that the study of dermatoglyphics is an objective aid in the clinical diagnosis of chromosomal dysmorphic syndromes. The dermatologlyphic patterns of four patients with trisomy 9p were analyzed and compared with dermatoglyphic data from 63 published case reports on the condition. We consider that the following traits constitute the combination of dermatoglyphic patterns that is specific to trisomy 9p: an excess of arches on the fingertips and toes, a low total finger ridge count, the absence of digital triradii b and c, and the presence of zygodactylous triradii z, z' and z'', a simian crease, a single crease on the 5th finger, a hypothenar crease, a distally placed axial triradius t', a proximal or tibial arch or both on the hallux, and increased intensity of the plantar patterns. A "phantom picture" is constructed, which can be used for dermatoglyphic diagnosis of the trisomy 9p syndrome.