Aim: To assess the long-term stability of orthodontic treatment and some factors associated to posttreatment changes. Methods: Six hundred twenty-seven dental casts of 209 patients were examined with the PAR Index at pretreatment (T1), end of treatment (T2), and at long-term follow-up (T3, mean 8.5 years posttreatment). Friedman test and multiple regression analysis at P < .05 were used to evaluate changes among the time points and factors associated with stability. Results: After orthodontic treatment, the PAR Index improved by 94.2%. No significant change was observed between T2 and T3 (P > .05). However, when the sample was divided into a well- (PAR Index ≤ 3) and a less well-finished (PAR Index > 3) group, it was observed that well-finished patients experienced some deterioration (P < .001), whereas the less well-finished ones showed some improvement (P < .05). Even with the deterioration, the well-finished patients still had a better PAR Index at T3 compared to the less well-finished ones. Regression analysis showed that PAR Index at T1 and T2, age at T1, and length of retainer wear had a slight association with occlusal stability (R2 = 0.27). No significant association was observed between stability and length of treatment, length of follow-up, sex, extraction, or third molar status on the other side. Conclusion: Orthodontic treatment is quite stable. Not so well-finished treatments tend to show some improvement and well-finished ones deteriorate some. Well-finished patients still have better occlusal characteristics. Retention contributes to maintenance of the final orthodontic results. World J Orthod 2010;11:61–66.