Aim: To evaluate the long-term result of chin-cap treatment in patients with a skeletal Angle Class III relationship due to mandibular prognathism. Material and Methods: Records of nine patients (five girls and four boys) with a mean age of 10.8 ± 1.6 years at the start of treatment were retrieved from the archives. The records comprised lateral cephalograms, intra- and extraoral photographs, and dental casts. The subjects were recalled at 6.1 ± 1.5 years after the completion of active orthodontic treatment. Cephalometric measurements from the treatment’s beginning (T1), end (T2), and follow-up (T3) were calculated by using PorDios software. Subjects with a positive overjet at T3 were grouped as stable, and those with a negative overjet were grouped as relapse. Differences between the two groups were analyzed by repeated measures analysis of variance (ANOVA) and the Duncan test. Results: Five individuals maintained a positive overjet at T3, while four relapsed as indicated by a negative overjet. SNA increased in the stable group between T2 and T3 but not in the relapse group. Conclusion: About half of the young individuals with a mandibular prognathism treated with a chin cap relapsed over time. The relapse seemed to originate from skeletal rather than dentoalveolar changes. World J Orthod 2009;10:317–322.