Background: The purpose of this study was to compare the efficacy of external levator advancement and Müller muscle–conjunctival resection in aponeurotic blepharoptosis repair. Methods: Mild to moderate blepharoptosis patients with good levator function and a positive phenylephrine test were randomized to upper blepharoplasty with either external levator advancement or Müller muscle–conjunctival resection. The primary outcome was marginal reflex distance 1 at 1 month after surgery. Secondary outcomes were cosmetic outcome, complications, and operating room time. Results: Forty patients were enrolled, six men and 34 women, with an average age of 62.4 years. The mean preoperative marginal reflex distance 1 in the levator group (39 eyes/20 subjects) and the Müller group (38 eyes/20 subjects) was 1.2 ± 0.8 mm and 1.5 ± 0.7 mm, respectively. The mean postoperative marginal reflex distance 1 in the levator and Müller groups was 3.0 ± 1.0 mm and 3.2 ± 1.0 mm, respectively. The difference in the mean change was 0.008, and was not statistically different (95 percent CI, −0.59 to 0.61; p = 0.978). The mean cosmetic outcome was 2.69 ± 0.81 for the levator group and 3.07 ± 0.68 for the Müller group, with a mean difference of 0.373 (95 percent CI, 0.06 to 0.69; p = 0.020). The average operating room time was 75 ± 19.2 minutes for the levator group and 71 ± 23.6 minutes for the Müller group (p = 0.439). There were four eyes that underwent reoperation, three in the levator group (7.7 percent) and one in the Müller group (2.6 percent). Conclusions: External elevator advancement and Müller muscle–conjunctival resection are both effective in correction of mild to moderate blepharoptosis. However, Müller muscle–conjunctival resection yields a statistically significant better cosmetic outcome and causes less eyelid asymmetry. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, II.