Objective: This study aimed to compare the long-term occlusal stability in patients treated orthodontically with and without occlusal adjustment. Material and Methods: This observational study followed the STROBE guidelines. The sample comprised 77 patients with class I malocclusion treated without dental extractions and without signs and symptoms of temporomandibular joint dysfunction (TMD), divided into two groups. Group 1 with occlusal adjustment comprised 37 patients, 16 males and 21 females, with mean initial, final, and post-retention ages of 18.33 (s.d.=3.96), 20.99 (s.d.=3.33), and 25.79 years (s.d.=3.34), respectively. The treatment time was 2.66 years (s.d.=1.57), and the time of post-retention evaluation was 4.80 years (s.d.=1.10). Group 2, without occlusal adjustment involved 40 patients, 21 males and 19 females, with mean initial, final, and post-retention ages of 18.07 (s.d.=3.03), 20.75 (s.d.=3.54), and 25.89 (s.d.=3.73) years, respectively. The treatment time was 2.68 years (s.d.=1.09) and the time of post-retention evaluation was 5.14 years (s.d.=1.36). The PAR and Little irregularity indices were measured in the initial, final, and post-retention dental casts. Intergroup comparison was performed using the independent t-test. Results: There was no statistically significant difference observed in the intergroup comparison of the PAR and Little irregularity indexes in all phases and periods evaluated. Conclusion: There was no significant difference found in the long-term post-treatment crowding and occlusal relapse between class I patients treated with orthodontic non-extraction with and without occlusal adjustment. The occlusal adjustment did not influence the alignment and occlusal post-retention stability.