This study was undertaken to establish normative values for mesio-distal crown dimensions of permanent teeth in some Nigerians. The mesio-distal crown dimensions of permanent teeth of two hundred and fifty secondary school students in Ibadan metropolis were measured. The sample size consisted of 125 males and 125 females selected by modified random sampling technique. Their ages ranged between 12 and 15 years. The mean value for each tooth size was recorded and can be regarded as normal values for the study population. The largest tooth in the mouth was the 1st mandibular molar in males while the smallest tooth was the lower central incisors in females. These normal values could be used as standard reference table for tooth sizes which will be of great importance to the orthodontist for the space analysis, to the prosthodontist for correct choice of teeth and to other disciplines like anatomy and anthropology.