Purpose: To quantify retinal nonperfusion area and retinal vascular bed area (RVBA) in mm(2) on ultra-widefield fluorescein angiography in eyes with diabetic macular edema (DME) and explore their relationship with the severity of DME. Methods: Prospective, observational case series. Baseline ultra-widefield fluorescein angiography images of 40 eyes from 29 patients with treatment-naive DME who participated in the DAVE study (NCT01552408) were stereographically projected at Doheny Image Reading Center. The retinal vasculature was automatically extracted to calculate RVBA. Nonperfusion area was manually delineated by two masked certified graders. Retinal vascular bed area and nonperfusion area were computed in mm(2) automatically by adjusting for peripheral distortion and then correlated with the severity of DME. Results: The global RVBA for the entire retina in eyes with DME was increased compared with healthy controls (54.7 +/- 16.6 mm(2) vs. 37.2 +/- 9.9 mm(2), P < 0.001) and correlated with the severity of DME (P < 0.05). Retinal ischemia (nonperfusion area) was nonuniformly distributed and not related to DME extent (P > 0.05). Conclusion: Eyes with DME have an increased RVBA compared with healthy controls. The severity of DME appears to be related to global RVBA, but not to retinal ischemia.