Based upon the present study the following conclusions were reached: Supervised toothbrushing with instruction for preschool children significantly and consistently decreased dental plaque scores, when compared to the control group of the same children who had only supervision. While those subjects receiving toothbrushing instructions and supervision had significant plaque reductions, at no time did the plaque scores reach zero. A symmetrical but nonuniform distribution of dental plaque prior to toothbrushing was noted as follows: Posterior teeth had higher dental plaque scores than anterior teeth. More dental plaque was present on the buccal surfaces of the maxillary teeth than on the lingual surfaces. More dental plaque was present on the lingual surfaces of the mandibular teeth than on the buccal surfaces. The distribution of dental plaque following toothbrushing remained the same as the prebrushing pattern, but the amount of dental plaque was reduced by 31 percent. Constant reinforcement is necessary to maintain effective plaque control in pre-school children.