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Management of large-size retrorectal gastrointestinal stromal tumors (GISTs) is complex and challenging from diagnosis to treatment. This may create technical difficulties in surgical access and complete resection of the tumor. The abdominosacral resection has the benefit of improved visualization via the anterior incision, with enhanced exposure of the midrectal area, which makes resecting the tumor completely via the posterior approach easier. We report 2 cases of patients with a retrorectal GIST and neurofibromatosis type 1, one in a 27-year-old woman with a defecation complaint and the other in a 58-year-old woman with a defecation and urination complaint. Based on the anatomical pathology, both patients were diagnosed with a GIST. The tumors were excised via an abdominosacral resection. Retrorectal GISTs are rare, and abdominosacral resection allows complete resection of a large-size retrorectal GIST with low morbidity and an absence of functional impairment. The abdominosacral resection should be considered in certain situations.