Background: Elderly patients are at high risk of both ischaemic and bleeding events, and the low body weight is considered a risk factor for major bleeding in atrial fibrillation (AF) patients on anticoagulation therapy. The aim of our study was to compare the safety and effectiveness of non-vitamin K antagonist oral anticoagulants (NOACs) versus well-controlled vitamin-K antagonists (VKA) therapy among AF patients aged >75 years and with a body weight <60 kg in a prospective registry setting. Methods: Data for this study were sourced from the Italian cohorts of PREFER in AF and PREFER in AF PROLONGATION registries. The occurrence of a composite of stroke, transient ischemic attack and systemic embolism (thromboembolic events) was the primary effectiveness endpoint. The occurrence of major bleeding was the primary safety endpoint. All-cause hospitalizations and all-cause death were the secondary endpoints. The net clinical benefit (NCB) was calculated in order to obtain an integrated assessment of the anti-thromboembolic and pro-haemorrhagic effects of NOACs vs. VKA. Results: Overall, 522 patients were included; 225 were on treatment with NOACs and 317 patients with VKA. The NOAC group more frequently featured a higher BMI and a higher prevalence of history of stroke/TIA and insulin-requiring diabetes; conversely, heart failure and chronic liver disease were less frequent in the NAOC group. In the unmatched study population, 18 patients (3.6% in the NOAC vs. 3.2% in the VKA group, p = 0.79) experienced thromboembolic events; 19 patients (1.78% in the NOAC vs. 4.73% in the VKA group, p = 0.06) experienced major bleeding events; and 68 patients were hospitalized during the follow-up (9.3% vs. 14.8%, p = 0.06). After balancing for potential confounders by using the 1:1 propensity score matching technique, 426 patients (213 on NOAC and 213 on VKA) were selected. We found no significant differences in terms of thromboembolic events (3.76% vs. 4.69%, p = 0.63), major bleeding events (n: 1.88% vs. 4.22%, p = 0.15) and hospitalizations (9.9% vs. 16.9%, p = 0.06) between NOAC vs. VKA matched population. Based on these incidences, we found a positive net clinical benefit (+1.6) of NOACs vs. VKAs. Conclusions: These real-world data suggest the safety and effectiveness of using NOACs in elderly patients with low body weight.