OBJECTIVE To report long-term rates of tumor control after radiotherapy (RT) for carcinoma in situ (CIS) of the true vocal cords (TVC). A comprehensive literature review was performed, and outcomes with other modalities of treatment for CIS of the TVC were compared. METHODS Thirty patients with CIS of the TVC were treated between July 1967 and May 1998 with curative intent using megavoltage RT. Most patients (28 of 30) were treated with cobalt-60 through small (usually 5 x 5 cm) fields. Median RT dose was 56.25 Gy (range, 56.25-75 Gy; mean dose, 59.15 Gy) at 2.25 Gy per fraction. One patient was treated for a synchronous head and neck primary malignancy with large fields to a total dose of 75 Gy at 1.8 Gy per fraction. Approximately two thirds of the patients (19 of 30) were referred for RT because of recurrence after at least one stripping procedure. RESULTS With a mean follow-up of 7.1 years (range, 2-17 years), the 5-year rates of local control, local control with larynx preservation, and ultimate local control (including salvage surgery) were the following: 88%, 88%, and 100%, respectively. Invasive squamous cell carcinoma developed in three (10%) of the patients. Time to failure was 14 months, 34 months, and 48 months, respectively. All three patients were surgically salvaged with a total laryngectomy. Cause-specific survival at 5 years was 100%. There were no late complications. CONCLUSIONS RT to approximately 60 Gy at 2.25 Gy per fraction using small (5 x 5 cm) fields produces excellent results with CIS of the TVC.