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Introduction: Clinical literature describing the in-patient use of bioscaffolds across the diverse spectrum of surgical specialties where these products are commonly used is typically limited to case series and retrospective analyses. At Boswick 2025, we outlined the design of the MASTRR Registry, a prospective multi-center study that was established to gain better insights into the safety of efficacy of ovine forestomach matrix grafts across a range of surgical procedures. The study design enables prospective patient data to be captured in the everyday use of OFM grafts, thus enabling multiple sub-analyses based on etiology, comorbidities, adjunctive therapies, and other variables, to establish a more comprehensive analysis of the scaffold’s safety profile and clinical effectiveness. Purpose: The purpose of the interim analysis is to present detailed findings from the first 432 patients enrolled in the MASTRR Registry, where OFM grafts were used as part of standard surgical soft tissue reconstruction. Methods: The prospective study was approved by a central IRB (Advarra, PA; NCT05243966) to enable prospective enrolment into an observational study across multiple investigational sites. The primary endpoint is proportion of treatment emergent adverse events (AEs). Each AE was investigated to establish severity and causality, according to ISO14155. Patients are monitored postoperatively for healing and AEs, with visits minimally at week 1, 4, and 12, and continued follow up until deemed healed or lost to follow up. This interim analysis represents the first 432 patients enrolled across 10 US sites, whose surgical procedure was conducted between May 2022 and June 2025. Results: A total of 432 patients were enrolled in the study, with n=7 screen failures. Of the n=425 (Safety population, SP) who underwent a procedure that used OFM grafts, n=14 were lost to follow-up (LTFU) immediately after the index procedure, leaving a total of n=411 in the Intent to Treat (ITT) population. Of these participants, n=400 (Per Protocol population) completed follow up for 14 days or more. For the SP, a total of 53 patients reported one or more AEs (12.5%), and there were a total of 63 unique AEs reported. The most common AEs were dehiscence (~3.1%), superficial infection (~2.8%), infection (~2.4%) or death (~2.4%). Importantly, all AEs were concluded to be unrelated (80.6%) or unlikely (17.7%) to be related to the OFM graft. A single (~0.2%) AE, ‘allergic reaction’ was concluded to ‘probably’ be related to the OFM graft, though this could not be confirmed via pathology. There were no reported incidents of graft loss. From the PP population (n=400 patients), patients had a median of one defect per patient (range; 1, 5) giving a total of n=464 defects. This included many defect types including burns (8.6%), DFU (22.1%), fistulae (9.5%), NSTI (2.9%), ostomy takedowns (10.9%), pilonidal sinus (10.7%), pressure injury (9.1%), surgical dehiscence (4.0%) and defects resulting from trauma (16.4%). Sub-group analysis of efficacy outcomes has shown the time to tissue coverage or fill of 2-4 weeks, depending on the extent of the defect and patient factors, and is consistent with prior published studies. Conclusion: This interim analysis of OFM grafts from a large prospective study has demonstrated that these devices have a low complication rate, and are clinically efficacious. Applicability to research/future/clinical practice: To the authors knowledge, this interim analysis is the largest collection of prospective data describing the use of a bioscaffold in inpatient soft tissue reconstruction procedures. The study design has enabled comprehensive analysis of safety and efficacy.