In patients with head and neck cancer, posttreatment imaging can be complicated and difficult to interpret because of the complexity of the surgical procedures performed and the postirradiation changes, but such imaging is critical for the evaluation of (a) the response to therapy and (b) tumor control. Posttreatment changes are affected by the type of surgery performed, reconstruction, neck dissection, and radiation therapy. Three types of flaps are used for reconstruction in the head and neck region: (a) the local flap, with geometric repositioning of adjacent tissue; (b) the pedicle flap, with rotation of donor tissue and preservation of the original vascular system; and (c) the free flap, with transfer of tissue that is revascularized by using microvascular surgical techniques. The posttreatment imaging findings in patients with head and neck cancer can be divided into four groups: altered anatomy secondary to surgical reconstruction, tumor recurrence, potential postsurgical complications, and possible postirradiation changes. Potential postsurgical complications are wound infection, abscess, fistula, flap necrosis, hematoma, chylous fistula, and serous retention. Possible postirradiation changes include mucosal necrosis, osteoradionecrosis, radiation-induced vasculopathy, radiation pneumonitis, radiation lung fibrosis, radiation-induced brain necrosis, and radiation-induced secondary malignancies. A familiarity with the imaging characteristics of posttreatment changes and of the potential complications caused by surgery and irradiation and an ability to differentiate these findings from tumor recurrence are essential for posttreatment surveillance and follow-up management of patients with head and neck cancer.