The effect of premature extractions of primary molars on further development of their successors was studied. A group of forty-six children with fifty-three unilaterally extracted mandibular primary molars was examined when the successors completed their root development. Radiographs of the successors to the extracted molars and their antimeres, which served as internal controls, were taken using the long-cone technique. Crown and root length and area in cross-section, were measured from tracings of the studied teeth and crown/root ratios were calculated. Significantly (p less than 0.05) larger area ratio in the extraction group was found suggesting a smaller root area. In addition, root foreshortening for the first premolars and diminished root area for the second premolars, both successors to teeth extracted after the age of eight years, were found. Although statistically significant, all of the differences were of no clinical importance.