Facial asymmetry is a naturally occurring phenomenon that is often due to differences in the mandibular dimensions on the right and left sides. The point where normal asymmetry turns abnormal cannot be easily defined, and no standards exist by which a judgement of abnormality can be made. The aim of the present study was to assess mandibular asymmetry in healthy children and its possible fluctuation during growth. The subjects consisted of 182 healthy children (88 girls, 94 boys) who had had an orthopantomogram taken at ages 7 (mean 7.5 years) and 16 (mean 15.9 years). On digitized orthopantomograms, condylar and ramus heights on both mandibular sides were measured with a Numonics Accugrid digitizer (Numonics Co., Montgomeryville, Pa., USA) and analysed with X-metrix software (Smart Systems, Turku, Finland). A paired t-test was used to determine the significance of the differences between the sides, and ANOVA to test the significance of the change in asymmetry during growth and between genders. The results revealed a statistically significant difference between the right and left sides in condylar height at age 7 years, in ramus height at both ages, and in the condylar and ramus height at age 16 years. The present study confirms that healthy young subjects generally have a statistically significant mandibular asymmetry, which, however, is only seldom clinically significant. The decision to initiate treatment because of asymmetry has to be carefully considered, since the study further showed that mandibular asymmetry may diminish or appear during growth of healthy subjects.