Background: To assess the configuration of primary and recurrent synovial sarcoma on MRI. Additionally, to evaluate postoperative MRI regarding diagnostic performance and locoregional post-treatment changes.Methods: Twenty-five patients with histologically proven synovial sarcomas underwent 1.5-T MRI follow-up between 2012 and 2018. In all, 258 pre- and postoperative MRIs with available radiological and pathological were screened for primary/recurrent synovial sarcoma, diagnostic performance (false-positive/-negative and true-positive/-negative values) and post-treatment changes.Results: The median age of the patients was 40±15.2 years. The median volumes of primary and recurrent synovial sarcomas were 603 cm3 and 806 cm3, respectively. Of the patients 24% presented recurrences (n=6). In two patients false-positive diagnosis was made . There was one false-negative diagnosis of synovial sarcoma. Primary synovial sarcomas were significantly most often polycyclic/multilobulated (p=0.01) and heterogeneous in appearance with marked contrast enhancement. Recurrent synovial sarcomas showed two appearances: ovoid/nodular/homogeneous and polycyclic/multilobulated/heterogeneous, both with marked contrast enhancement. The most common post-treatment changes were subcutaneous (92%; p<0.001) and muscular edema (72%; p<0.001-0.003). Conclusion: While the configuration of primary synovial sarcomas was mainly polycyclic/multilobulated/heterogeneous, recurrent synovial sarcomas showed two shapes: ovoid/homogeneous and polycyclic/multilobulated/heterogeneous. MRI is still a highly valuable imaging modality for the postoperative surveillance of synovial sarcomas. Subcutaneous and muscular edema are common post-treatment changes.