Purpose: To investigate the efficacy of aflibercept for the treatment of diabetic macular edema via a treat-and-extend regimen. Methods: This prospective, single-center, open-label, interventional study involved 30 patients with a best-corrected visual acuity (BCVA) ≤0.6 and a central retinal thickness (CRT) ≥300 μm. The enrolled eyes each received a monthly intravitreal aflibercept injection until the CRT decreased below 300 μm, upon which the administration interval was extended for 1 month until the CRT once again increased to ≥300 μm. Main outcome measures were median BCVA and CRT at 6 and 12 months after initiation of treatment via last observation carried forward analysis, the median number of injections over the 12 months, and the effects on the diabetic retinopathy severity scale (DRSS) score of the patients who completed the 12-month follow-up period. Results: Of the 30 enrolled patients, 29 and 25 respectively completed the 6- and 12-month follow-up examinations. From baseline to 6 and 12 months after treatment initiation, the median BCVA (logarithm of the minimum angle of resolution) significantly improved from 0.52 to 0.30 and 0.35, respectively, and the median CRT significantly decreased from 439.5 to 268.5 and 249.0 μm, respectively. The median number of injections over the 12-month follow-up period was 6.0. Compared to baseline, the DRSS score at 12 months was improved by 2 steps in 16% of patients; in no cases did the DRSS score worsen or improve by three steps or more. Conclusions When administered in a treat-and-extend regimen, aflibercept is an effective treatment option for diabetic macular edema.