This study was conducted to measure the mesio-distal width of mandibular incisors and maxillary and mandibular canines and premolars of 200 Egyptian adolescents with an age range from 12 to 15 years selected randomly from three different hospitals in Alexandria governorate. All selected subjects were free from morphological anomalies, apparent orthodontic problems and proximal caries.Upper and lower impressions were taken. Each impression was poured immediately by dental stone. Mesio-distal widths of mandibular incisors and maxillary and mandibular canines and premolars were measured from the study models using an electronic digital caliper. Data were collected and statistically analyzed. The results of this study revealed that: There was a statistical significant difference in the mean mesio-distal teeth widths between boys and girls for all the mandibular and maxillary teeth.No statistical significant difference was observed between the mean mesio-distal widths of the teeth on right and left sides in boys and girls.Positive significant correlation between the mesio-distal widths of upper canines and premolars with the lower incisors was recorded in boy and girls.Positive significant correlation between the mesio-distal widths of upper right canine and premolars with the upper left canine and premolars was evident in boys and girls.Positive significant correlation between the mesio-distal widths of lower canines and premolars with the lower incisors was revealed in boys and girls.Positive significant correlation between the mesio-distal widths of lower right canine and premolars with the lower left canine and premolars was observed in boys and girls.Positive significant correlation between the mesio-distal widths of upper canines and premolars with the lower canines and premolars was found in boys and girls.A new prediction equations were concluded and proposed from the results of this study sample.From the results of this study we can conclude that:Due to sexual dimorphism found in this study sample, the mesio-distal teeth widths should be measured separately in boys and girls.No teeth size discrepancy between right and left sides in boys and girls. So, if teeth on one side are missing, the measurements of teeth in the other side can be used interchangeably to represent the missing teeth.Due to the positive correlation found between mesio-distal widths of upper and lower canines and premolars and lower incisors so, we can predict the mesio-distal width of unerupted canines and premolars by measuring the early erupting lower incisors.Based on the data obtained from this study, a prediction equation was proposed to give better accuracy for the study sample than Tanaka and Johnston’s equation.