Blepharoptosis with coexisting strabismus can be observed in adults, and both these conditions affect cosmetic appearance and have psychosocial effects. Both also commonly require surgery, which is typically performed using a sequential approach. This study aimed to evaluate the efficacy of simultaneous Müller's muscle-conjunctival resection with or without tarsectomy and strabismus surgery in adult patients with ptosis and coexisting strabismus. Patients with ptosis and coexisting strabismus who underwent simultaneous Müller's muscle-conjunctival resection with or without tarsectomy and horizontal strabismus surgery were retrospectively evaluated. Analysis included measurement of the angle of deviation in prism diopters, margin reflex distance, eyelid height asymmetry, and complications following surgery. Success of Müller's muscle-conjunctival resection with or without tarsectomy was defined as a margin reflex distance of ≥3.5 and ≤5 mm with a difference between the two upper eyelids of <1 mm. Strabismus success was defined as alignment with ±10 prism diopters of orthotropia. The patients comprised three women and five men with a mean age of 37.12 years (range, 22-62 years). The strabismus stage of the surgery was performed first in all patients. Upper eyelid symmetry outcomes were assessed as perfect (<0.5 mm) in four patients and good (≥0.5 mm, <1 mm) in four patients. Success of Müller's muscle-conjunctival resection with or without tarsectomy was achieved in six of eight patients (75%), and strabismus success was achieved in all patients. No revision eyelid or strabismus surgery was required following simultaneous surgery in any of the patients. Müller's muscle-conjunctival resection with or without tarsectomy combined with strabismus surgery may be an alternative approach for use in patients with ptosis and coexisting strabismus.