Questions concerning subsequent pregnancies invariably arise in the minds of parents who have produced a malformed child, or one suffering the effects of a familial disease. The obvious source of information and advice in such situations is the physician, and he is required to discuss among many other things, the probabilities of repetition of the same event. This calls for a wide knowledge of genetics and teratology, in fact for a body of information which is not yet available to us, except in relatively few instances.