The records of 40 consecutive patients treated at the Princess Margaret Hospital (PMH) between 1979 and 1988 for aggressive fibromatosis were reviewed. The median follow-up was 86 months (range 21-167 months). All surgery was performed at the referring hospitals. Thirty-six underwent an attempt at excision, four were biopsied. Thirty-one had no overt disease after surgery and 26 of these received adjuvant irradiation. Eight were treated with radiotherapy alone, and another was treated with azathioprine and prednisone. Twenty-four (60%) presented with recurrent disease. The overall relapse free rate was 63% at 5 and 10 years. Combined surgery and irradiation had a higher relapse rate than irradiation alone (46% vs. 25%), and a high proportion of failures in the combined group were marginal failures (36%). Relapses following surgery alone were 1/5 (20%), and chemotherapy 0/1. Tumour size greater than 8 cm predicted for relapse (p = 0.002), but tumour site, status of surgical margins, and presence or absence of a history of relapse were not statistically significant. Twelve with subsequent treatment failure underwent successful salvage surgery, and 37/40 (92%) were disease free at last follow-up. A functional assessment (modified Johnstone scale) revealed 11/24 patients (46%) with poor functional outcomes (grade 2 or less) after all treatment compared with 6/24 (25%) at referral. Ten of 11 (91%) with grade of 2 or less had a history of recurrence, and 4/5 amputations were for treatment of a painful recurrence. Treatment planning in this study was hampered by inadequate information on tumour location since few patients had clinically apparent disease when seen by the radiation oncologist (only 35% of cases) and fewer had preoperative cross-sectional imaging available (12% of cases).(ABSTRACT TRUNCATED AT 250 WORDS)