Introduction: Although there are numerous studies in the literature on alignment stability in the lower arch, there are few referring to the upper arch. Aims: To assess upper arch stability (irregularity index, widths and length of arch, overjet and overbite) in orthodontically treated patients by comparing late incisor stability with the initial malocclusion and type pf treatment undertaken. Study design: The study models of 51 patients, treated with or without extractions, were analysed at three different points in time: pre-treatment (T1), post-treatment (T2) and post-retention (T3) (average 5 years). The following parameters were measured: irregularity index, arch length, inter-canine and inter-molar widths, overjet and overbite. Results: The results showed that upper incisor crowding relapses, although a net improvement is noted in comparison to the initial state both in cases treated with or without extractions. The arch length also relapses in both cases. The inter-canine and inter-molar widths as well as the overjet and overbite are stable in the long term. The long-term response of maxillary incisor alignment is unpredictable. Conclusions: There is a statistically significant reduction in incisor irregularity, length and width of arch (inter-canine and inter-molar widths), whereas overjet and overbite undergo a reduction of little magnitude. No statistically significant correlation is noted between late incisor stability and the initial malocclusion or type of treatment.