In modern orthognathic surgery, the functional results cannot disregard a good aesthetic outcome. In this study, a stereophotogrammetric longitudinal analysis of the symmetry of facial thirds was performed in 18 patients affected by Class III skeletal malocclusion, with clinical asymmetry, treated with a bimaxillary osteotomy. Their 3-dimensional facial images were acquired in the preoperative phase and 6, 12, and 24 months after surgery, and compared to those obtained in a control group of 23 subjects with Class I skeletal occlusion, without clinical asymmetry and no history of traumas or alterations at the maxillo-facial area. Images of the hemi-faces of the subjects were divided into thirds (upper, middle, lower), mirrored and superimposed to their contralateral ones; soft-tissue facial symmetry was obtained as the root mean square distance between the hemi-faces in the three thirds.In patients, no significant differences in facial symmetry (root mean square distance) were found among the study time points (analysis of variance, P > 0.05); the lower facial third was more asymmetric than the upper one (Tukey honestly significant difference P < 0.05). Patients were significantly more asymmetric than the control subjects (Student t, P < 0.05). In conclusion, patients with Class III malocclusion exhibited a higher level of facial asymmetry than control subjects; their asymmetry did not change significantly in the different phases of the surgical and orthodontic treatment and throughout a 24-month follow-up. In skeletal Class III patients, bimaxillary osteotomy did not modify the level of asymmetry in any facial third.