The boom in genetics and, in particular, cytogenetics in the `60's has filled the shelves of our libraries. During the same period, however, only a handful of books on the best known of the chromosomal aberrationsmongolismhave been published. The appearance of a good book on mongolism is therefore most welcome. One of the authors, L. S. Penrose, has devoted over 30 years to this subject; the book reflects the special flavor which an original, and at times mathematically inclined, writer can bring to research.