Overall, 39 of a total of 79 patients underwent an MRI follow-up scan after resection of primary aggressive fibromatosis (AF) for a minimum of 1 year. The recurrent tumor was examined for contrast agent behavior, appearance, and extent in MRI. The patients were divided into two groups: younger and older than 25 years of age. The median recurrence-free follow-up interval was 49 months. Sixteen patients had no recurrence, and in 15 patients the suspicion was later withdrawn. Recurrences occurred in eight patients (21%), thus a high sensitivity but a moderate specificity (0.561) for the MRI scan. Recurrences occurred significantly more often during the first 9 months of the follow-up scan and especially in patients < 25 years of age. There was no significance in the appearance of AF, with a fascicular character the most common feature of recurrent AF. The primary tumors were altogether significantly smaller than recurrent AF. Muscle edema occurred significantly more often in patients with recurrences than in patients without them. The status of resection (R0Â–2) had no impact on recurrent AF. We showed that MRI follow-up scans result in a high sensitivity but a moderate specificity for the detection of recurrent AF because the distinction between recurrent AF and posttherapeutic changes is often difficult. Further studies are needed to investigate the radiologic features of recurrent AF and risk factors detected on MRI.