The purpose of this study was to determine the amount of fluoride dentifrice ingested by mentally handicapped children during toothbrushing. A group of 24 mentally handicapped children, aged between 3 and 12 years, were used in the study. They were encouraged to brush in their usual way with a sodium fluoride dentifrice from a preweighed tube. Rinsings and excell dentifrice were collected, and fluoride analyses were performed on the rinsings and controls. The amount of fluoride retained was in the range of 14 to 269 ug, with a mean of 87 ug, equivalent to a mean retention of 23.5% of dentifrice. This is similar to findings of studies of children of normal intelligence. Thus, fluoridated dentifrices should be used by mentally handicapped children, but, as with all young children, small amounts of dentifrice should be used, preferably under direct adult supervision.