The Canadian Motherisk Program is so well-organized that it can he regarded as a representative teratogen consultation system outside of Japan. The Toranomon Hospital S system is a similar system within Japan. By studying various characteristics of the two systems an optimal system was proposed with an innovative risk calculation formula. In the proposed optimal system, one should consider such factors as system follow-up, versatile computer back-up, global coverage of people, easy access to the system, wellcontrolled documentation, sufficient and up-to-date information collection, financial support by health insurance, manpower back-up in different specialties, and security protection. An innovative risk calculation formula is a product of risk points of the drug itself and administration-time risk points of the particular drug in question.