Purpose: To evaluate the impact of hormonal therapy on MRI characteristics of desmoid-type fibromatosis on T1-weighted, T2-weighted fat-saturated and post-contrast sequences. Materials and methods: Nineteen patients with histologically-proven desmoid-type fibromatosis were prospectively followed up on MR imaging. Eight patients underwent hormonal therapy and 11 were only surveyed. Change in tumor size during follow-up was analyzed according to RECIST. Signal intensity on T1-weighted, T2-weighted fat-saturated and T1-weighted fat-saturated post-contrast images was graded from 0 to 5 using adjacent normal muscle as reference. Findings were compared with tumor growth and treatment option. Results: There were seven men and 12 women with a mean age of 42.2±16.4 (SD) years (range: 18 - 64 years) yielding twenty-six follow-up periods: eight of tumor progression and 18 of tumor stability/regression (some tumors exhibited more than one behavior type). Hormonal therapy was associated with tumor stability or regression (P=0.0207). There was a significant reduction in enhancement among treated patients with stable/regressing disease (P=0.049). The mean variation in enhancement grade was -1.3±1.2 in these patients. All successfully treated patients presented a reduction in enhancement. Lesions with marked low enhancement or very low signal on T2-weighted images were rare in progressing lesions (0% and 13%). Conclusion: Hormonal therapy has an impact on desmoid-type fibromatosis signal characteristics reducing lesion enhancement.