Purpose: To evaluate the change in upper eyelid position after horizontal surgical tightening in patients with floppy eyelid syndrome. Design: Prospective, noncomparative, interventional case series. Participants: Eighteen patients with a clinical diagnosis of floppy eyelid syndrome. Methods: Horizontal surgical tightening of the upper eyelid was performed by full-thickness wedge resection in 24 eyelids of 18 patients with floppy eyelid syndrome. Preoperative and postoperative upper eyelid position as measured by the margin reflex distance (MRD) was assessed. Student's paired t test then was used to analyze the change in upper eyelid position after horizontal tightening alone of floppy upper eyelids. Main Outcome Measures: Change in upper eyelid MRD after surgery. Results: Preoperative MRD ranged from -0.5 to 4.0 mm, with a mean of 1.9 mm (±1.3 mm, standard deviation [SD]). Postoperative MRD ranged from 0.5 to 6.0 mm, with a mean of 3.2 mm (±1.4 mm, SD). The change in MRD ranged from -0.5 to 2.5 mm, with a mean of 1.3 mm (±0.7 mm, SD; P<0.001). Conclusions: Horizontal upper eyelid tightening alone generally results in secondary improvement of the ptosis associated with floppy eyelid syndrome.