Background <p>The biologic behavior of musculoskeletal fibromatoses is intermediate between that of benign and malignant fibrous lesions, as these tumors commonly demonstrate infiltrative growth that leads to frequent local recurrence but lack metastatic potential. Due to the high tendency of recurrence, post-therapeutic follow-up is essential. We aimed in this study to determine the additional value of contrast-enhanced magnetic resonance imaging (CE MRI) and quantitative diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) mapping over traditional magnetic resonance imaging in the post-therapeutic follow-up of musculoskeletal fibromatosis.</p> Patients and methods <p>This study included 64 patients with a total number of 67 lesions representing different types of musculoskeletal fibromatosis under post-therapeutic follow-up. DWI with ADC mapping was done followed by positioning the region of interest to encompass the lesion's largest possible area to calculate the ADC value.</p> Results <p>Pre-therapeutic musculoskeletal fibromatosis had mean ADC values of 1.2 (0.08–3.00) × 10⁻³ mm²/s and a minimum of 0.8 (0.0–2.7) × 10⁻³ mm²/s, while the post-therapeutic mean ADC value was 1.0 (0.02–2.4) × 10⁻³ mm²/s and a minimum of 0.2 (0.0–2.1) × 10⁻³ mm²/s. Analysis of the post-therapy follow‑up studies of fibromatoses showed that lesions with favorable responses to chemotherapy or radiotherapy exhibited significantly lower ADC values than those with progressive disease courses.</p> Conclusions <p>In the therapeutic follow-up of musculoskeletal fibromatoses, MR imaging is the imaging modality of choice. When determining the response to chemotherapy and radiotherapy, combined evaluation of the T2 signal intensity, degree of post-contrast enhancement, and ADC value has a higher sensitivity than relying solely on the size of the lesion in the traditional MRI.</p>