The striking parallel between the melanin pigmentary abnormalities of the hair and skin in piebaldism, Waardenburg's syndrome, piebaldism with deafness, and piebaldism or Waardenburg's syndrome with aganglionosis of the gut suggests that all these disorders belong to the same category. At present, the most logical way to link these syndromes is to consider them the results of defective development of the neural crest. The reason that in certain circumstances only melanoblasts are affected whereas in other situations other neural crest derivatives also are involved is not yet clear. In addition, some features, such as the upper limb abnormalities observed in Klein's syndrome, are not explained by a neural crest defect. Our knowledge of the interaction between the neural crest and neighboring structures closely related to it during embryonic life is limited. Some clues allowing us to better understand these complex syndromes combining depigmentation of hair and skin will come from future research in this field.