Purpose: The aim of this study was to assess the efficacy and safety of ranibizumab in patients with diabetic macular edema (DME). Methods: We conducted a retrospective analysis of consecutive patients with vision loss due to DME who were treated with ranibizumab. All patients received a loading dose of 3 monthly injections followed by re-treatments on an as-needed basis. The primary endpoint was the change in best-corrected visual acuity (BCVA) at 12 months. Secondary endpoints were the change in central retinal thickness (CRT) and the number of intravitreal injections (IVI) at 12 months. Results: One hundred and six eyes of 78 patients were included. BCVA changed from 48.3 (20/100) letters at baseline to 59.0 letters (20/63) at 12 months (p < 0.0001; mean gain: +10.7 letters), and 38% of the patients had a final BCVA >70 letters. CRT decreased from 519 µm at baseline to 355 µm at 12 months (p < 0.0001). The threshold of the first quartile of the baseline VA was 40 letters. Patients with a baseline VA >40 letters had a higher final VA of 66 ± 14 letters (20/50) versus 43 ± 18 letters (20/125) for patients with a baseline VA ≤40 letters (p < 0.0001). A mean number of 5.4 (3-10) IVI were administered. Conclusion: This study conducted in a clinical setting confirms the results of previous randomized trials. The final BCVA was mainly influenced by the baseline BCVA, which supports the utility of early DME treatment before patients experience a severe vision loss.