The type of imbecility with which my paper deals is chiefly met with in the special institutions and in the out-patient clinics of children's hospitals, and is fairly common in this country. The somewhat scanty literature of the subject, however, includes descriptions of the leading features of the class which differ a good deal in detail. This divergence of opinion is due, I think, mainly to the fact that observers are by no means agreed as to the degree of deviation from other types which qualifies an imbecile for inclusion in the Mongol group—a disagreement easy to understand when we realise that there is hardly one single feature which can be regarded as peculiar to Mongolism. Further, many recorded cases have been noted only at an early age, when certain later-developed aids to diagnosis are wanting. I have thought it of interest to record my observations of twenty-one well-marked cases met with among the 2000 inmates of Darenth Asylums, where the minimum age of admission is five, trusting that they may afford some guide to the mental and physical forecast advisable in dealing with the infant.