Fibromatosis is a benign lesion, which originates from proliferating fibroblasts. Although fibromatosis is a benign tumor, it is locally aggressive and invasive. Spinal presentation of fibromatosis is very rare, and case reports are the only source of the clinical knowledge. Herein, we describe the oldest patient having spinal fibromatosis with de novo occurrence and aggressive nature. A 68-year-old female patient admitted to our outpatient clinic with low back pain and neurological claudication. On lumbar spine magnetic resonance imaging, she had spinal canal stenosis with a concomitant lesion in the left longissimus muscle. We did our best to resect the tumor, entirely. The pathology result was consistent with spindle cell lesion. The lesion recurred 6 months after the primary surgery. In the second surgery, we did en bloc resection. Pathology and immunohistochemical analysis results were consistent with fibromatosis. After the second surgery, she had adjuvant radiotherapy. There was nothing other than radionecrosis in the operation site, still after 2 years. In conclusion, radiological work-up is usually insufficient to make fibromatosis diagnosis and whole pathological specimen should be carefully evaluated to achieve the accurate diagnosis. Spinal fibromatosis is very rare and its treatment methods have not universally been conceptualized. However, adjuvant therapies are necessary after en bloc resection.