The life and medical writings of Moses Maimonides have recently been commented upon.1One of the more popular of Maimonides' medical works is theTreatise on Hygienewhich was written in Arabic in 1199 at the request of the Sultan AlMalik Al Afdal, eldest son of Saladin the Great of Egypt. It was translated into Hebrew and Latin by Moses Ibn Tibbon and John Di Capua, respectively, in the 13th century. Recently, German2and English3,4versions as well as a new Hebrew edition5have appeared. However, Maimonides' other theological and rabbinic works also contain numerous references to personal and physical hygiene. In volume 1 of his massive codification of biblical and talmudic law, theMishneh Torah, an entire chapter is devoted exclusively to principles of hygiene. This, chapter 4 of the laws dealing with temperaments (Hilchoth De'oth), is presented here in its entirety, translated from the original