Purpose To evaluate the extreme peripheral retina and pars plana during vitrectomy in patients with proliferative diabetic retinopathy. Methods In a prospective study using a modified ophthalmic endoscopic system and an intraocular light source, we performed fluorescein angiography during pars plana vitrectomy in 12 eyes of 10 patients with proliferative diabetic retinopathy. Vitrectomy had been performed previously in two patients, and the subsequent surgery was necessary because of recurrent vitreous hemorrhage in one patient and silicone oil removal in the other. Results All 12 eyes of 10 patients demonstrated a wide avascular area in the peripheral retina anterior to the previous photocoagulation scar. At the ora serrata in two eyes, a fibrovascular ridge of peripheral retinal vessels with fluorescein leakage that resembled the demarcation line in retinopathy of prematurity was noted; one eye had developed neovascular glaucoma 4 weeks after vitrectomy with maximum augmentation of endolaser photocoagulation, and the other eye had neovascular glaucoma that had been treated with photocoagulation 1 year before vitrectomy. In the two eyes that had undergone previous pars plana vitrectomy, fluorescein leakage was apparent at the fibrous scar of the sclerotomy site. Conclusion Intraoperative fluorescein angiography using an endoscope disclosed unusual findings in the extreme peripheral retina and pars plana of patients with proliferative diabetic retinopathy. Intraoperative fluorescein angiography may aid intraoperative evaluation and treatment of proliferative diabetic retinopathy.