To evaluate the results of early interceptive grinding and also the possibility of self-correction of unilateral cross-bite, 76 4-yr-old children with this malocclusion were divided into one treated and one untreated group. In the treatment group 50% of the children exhibited a normal transverse occlusion evaluated in the mixed dentition, at the age of 9. In the untreated group only 17% showed a spontaneous correction of the cross-bite. Among the studied dental variables the "max./mand. arch width difference" especially in the canine region was found to be a valuable predictor indicating whether cross-bite can be successfully treated in preschoolchildren by selective grinding. The results of this study support early treatment of unilateral cross-bite and gives the criteria whereby successful treatment by selective grinding may be expected.