Surgical treatment for intra-abdominal/retroperitoneal desmoid-type fibromatosis (IA/RPDF) is still controversial. Studies regarding en bloc resection in IA/RPDF with adjacent organ involvement are scanty. This study aims to evaluate the safety and effectiveness of en bloc resection in IA/RPDF with adjacent organ involvement. This retrospective clinical study included 21 patients who were diagnosed with IA/RPDF and underwent tumor resection at a single center between March 2013 and June 2018. All patients included in the study underwent surgery with curative intent, and IA/RPDF with adhesive organs was removed en bloc. The safety of surgical treatment was verified by the analysis of intraoperative bleeding, postoperative morbidity and perioperative mortality. The efficacy of surgical treatment was evaluated based on the status of tumor infiltration of adjacent organs and patient follow-up results. Complete macroscopic (R0 or R1) resection was achieved in all cases. A median of 2 (range, 1-7) organs were resected. The median operating time was 300 (90-650) minutes. The median intraoperative bleeding was 300 (20-4,500) milliliters. For postoperative pathological diagnosis at our center, tumor infiltrated at least one organ in each patient. Infiltration was noted in 45 resected organs (45/57, 78.9%). Grade III-V postoperative morbidity developed in one patient (4.8%). During the follow-up, one patient developed local recurrence. No DF-related death was noted during the follow-up. The 3-year disease-free survival rate was 94.1% (95% confidence interval: 83.6-100%). Therefore, en bloc resection of the tumor and involved adjacent organs is a safe and effective treatment modality for IA/RPDF.