Local control rate by radical radiation therapy was analyzed in 33 patients with a piriform sinus cancer. Twenty-five patients (76%) were in stage T3 + T4. Local recurrence-free survival at 3 years was 49% in T1 + T2 and 25% in T3 + T4 (p = 0.01). In T1 + T2 lesions, a biologically effective dose for an acute reaction over 80 Gy and total treatment time less than 70 days appeared to improve local control. In T3 + T4 lesions, good radiation response assessed by the regaining of laryngeal mobility affected local control favorably. An esophageal involvement and destruction of the laryngeal cartilage as well as soft tissue extension precluded the possibility of local control by radiation therapy alone. In addition to the T-stage, other tumor factors should also be considered for predicting local control with radiation therapy.