Objectives: We set out to determine the optimal treatment options—surgery, radiation therapy (RT), systemic therapy, or any combinations thereof—for patients with desmoid tumours once the decision to undergo active treatment has been made (that is, monitoring and observation have been determined to be inadequate); provide clinical-expert consensus opinions on follow-up strategies in patients with desmoid tumours after primary interventional management. Methods: This guideline was developed by Cancer Care Ontario’s Program in Evidence-Based Care and the Sarcoma Disease Site Group. The MEDLINE, EMBASE, and Cochrane Library databases, main guideline Web sites, and abstracts of relevant annual meetings (1990 to September 2012) were searched. Internal and external reviews were conducted, with final approval by the Program in Evidence-Based Care and the Sarcoma Disease Site Group. Recommendations: Treatments: Surgery with or without RT can be a reasonable treatment option for patients with desmoid tumours whose surgical morbidity is deemed to be low; The decision about whether RT should be offered in conjunction with surgery should be made by clinicians and patients after weighing the potential benefit of improved local control against the potential harms and toxicity associated with RT; Depending on individual patient preferences, systemic therapy alone or RT alone might also be reasonable treatment options, regardless of whether the desmoid tumours are deemed to be resectable. Follow-Up Strategies: Undergo evaluation for rehabilitation (occupational therapy or physical therapy, or both); Continue with rehabilitation until maximal function is achieved; Undergo history and physical examinations with appropriate imaging every 3–6 months for 2–3 years, and then annually.