Purpose: To investigate the alterations of macular thickness during and after panretinal photocoagulation (PRP) in patients with severe diabetic retinopathy and good vision, and to compare the outcomes of weekly and biweekly treatments. Design: Prospective, comparative interventional case series. Participants: Thirty-six patients with severe nonproliferative diabetic retinopathy or non-high-risk proliferative diabetic retinopathy whose visual acuity was 20/20 or better before PRP. Methods: Seventy-two eyes of 36 patients underwent scatter PRP in 4 sessions. The macular thickness was measured by optical coherence tomography. The photocoagulation sessions were performed weekly to one eye and biweekly to the other eye. Each eye was selected at random. Main Outcome Measures: Best-corrected visual acuity and macular thickness. Results: Visual acuities were maintained in 89% of eyes with weekly treatments and 92% of eyes with biweekly treatments. Macular thickness was increased transiently in the central macula in both eyes, more in the weekly treated eyes, and then decreased to control levels in eyes treated biweekly but remained thickened in eyes treated weekly. Conclusion: For eyes with severe diabetic retinopathy and good vision, PRP with either weekly or biweekly treatment did not affect postoperative visual acuity. However, biweekly treatments allowed faster recovery of macular thickening after PRP than weekly treatments.