BACKGROUND Treatment algorithms for patients with aggressive fibromatosis (AF) are challenging. There are limited data available about the use of systemic therapy (ST) in pediatric patients with AF. METHODS Patient-, tumor-, and treatment-related factors of 90 children and adolescents with AF treated on multiple prospective trials of the Cooperative Weichteilsarkom Studiengruppe (1981-2015) were analyzed with focus on response and outcome of ST. RESULTS Median age was 9.48 years (0.02-18.05). Primary resection was performed in 54 patients and ST was administered in 29 of 54 patients because of disease progression or relapse. In 35 patients, ST was the initial treatment modality. A secondary resection was performed in 21 of 35 patients after ST. A total of 64 patients received ST, mainly methotrexate and vinblastine (40%) with a median duration of 380 days. The most frequent radiological response to ST was stable disease at 3 months (39%) and partial response at 6 months (53%). Radiotherapy was administered to 15 of 90 patients. One patient remained on observation only. The 5-year overall survival was 100% and the 5-year event-free survival (EFS) was 44%. Patients who had a primary resection showed a 5-year EFS of 35% versus 59% in patients who had received primary ST (P = 0.08). Functional deficiencies as long-term sequelae following resection occurred in 11 patients. At a median follow-up of 5.05 years (0.25-14.88), complete remission was achieved in 51 patients and partial remission in 28 patients. CONCLUSIONS ST seems appropriate if a primary complete resection is not feasible and at relapse/progression after resection.