ABSTRACT Purpose: To compare the surgical results of adjustable and non-adjustable horizontal strabismus surgery for concomitant horizontal strabismus. Methods: The charts of 231 patients, who underwent horizontal strabismus surgery, selected using probabilistic sampling, were retrospectively reviewed. Patients were divided into two groups according to the surgical technique used and strabismus type. The adjustable suture technique was used for 107 patients (Group 1), and non-adjustable or conventional surgery was performed in the remaining 124 patients (Group 2). Patients with esotropia (ET) or exotropia (XT) of <55 prism diopters (PD) at distance were included. The following exclusion criteria were applied: all intermittent or vertical deviations, anisotropias >5 PD, syndromes, restrictive or paretic strabismus, reoperations, botulinum toxin injection, and patients postoperatively followed up for <3 months. Surgical success was set to a range between orthotropia and an esodeviation of up to 10 PD for both ET and XT. Results: An amblyopia rate >50% was present in all subgroups. Significant differences between strabismus groups submitted to adjustable technique and non-adjustable on postoperative day 1 were observed (p=0.00 for ET and p=0.01 for XT) and at the last visit for the XT group with a follow-up of at least 1 year (p=0.05). Conclusion: The adjustable suture technique produced a higher success rate than non-adjustable strabismus surgery for both ET and XT groups on postoperative day 1. For XT patients, the adjustable suture technique appears to produce better surgical results than non-adjustable surgery, when the surgical goal is long-lasting maintenance of a small hypercorrection.