Objective: In conjunction with appropriate wound care, negative pressure wound therapy with instillation and dwell time (NPWTi-d) may be used as an adjunct therapy for acute or hard-to-heal (chronic) wounds, especially when infected. However, there are very few data on the use of NPWTi-d in the treatment of fibrinous wounds that are difficult to debride mechanically. The main objective of this study was to describe changes in the fibrin area of such wounds, before and after treatment with NPWTi-d. Method: This was a monocentric, observational, prospective pilot study evaluating the NPWTi-d medical device. Eligible patients included in the study were those with hard-to-heal lower limb ulcers who had previously undergone unsuccessful specific debridement treatment for their wound, with failure of manual mechanic debridement for at least six weeks' duration, and whose wounds had a fibrinous surface area of >70% of the total wound surface area. The primary endpoint was the difference in the percentage of fibrinous surface area before and after treatment. Results: A total of 14 patients who received treatment for lower limb ulcers between October 2017 and August 2019 were included in the study. There was a significant shrinkage rate of the fibrinous wound surface between the start and end of treatment (83.6±14.5% and 32.2±19.7%, respectively; p<0.001). Conclusion: This study showed a significant decrease in fibrin area in wounds treated with NPWTi-d, with good tolerance. We believe that NPWTi-d has its place in the multidisciplinary management of patients with hard-to-heal ulcers. Additional randomised studies are required to confirm these findings. Declaration of interest: The authors have no conflicts of interest.