To evaluate the predictive value of the adjacent sign (Fig. The tumor adjacent to the thyroid cartilage on radiological examinations) in the newly published sixth edition of the International Union Against Cancer (UICC) staging system of glottic carcinoma. From 1989 through 1997, 130 patients with T1-2N0 glottic squamous cell carcinoma classified by the fifth edition of the UICC staging system, evaluated with radiological examinations (CT and/or MR), were treated with radiation therapy (RT). Factor analysis for local control included clinical characteristics (age, T stage in the fifth edition, tumor shape, vocal cord mobility, and involvement of anatomic subsites), radiological findings (tumor size and adjacent sign), and treatment characteristics (total dose, fraction size, field size, overall treatment time, and interruption of treatment). Tumors with the adjacent sign, which should represent paraglottic space invasion with/without minor thyroid cartilage erosion, were retrospectively classified as T3 stage in the sixth edition of the UICC staging system. The 5-year local control rate following RT was 76%. Univariate analysis showed that the T stage in the UICC fifth edition, supraglottic extension, subglottic extension, tumor size, adjacent sign, total dose, fraction size, field size, and overall treatment time were significant factors for local control rate. Multivariate analysis confirmed the adjacent sign as only an independent predictor. According to the sixth edition of the UICC staging system, the 5-year local control, laryngeal preservation, cause-specific survival, and overall survival rates of the T3 (adjacent sign positive) vs. the T1 and T2 (adjacent sign negative) lesions were 37% vs. 87% (p < .0001), 47% vs. 95% (p < .0001), 75% vs. 99% (p < .0001), and 54% vs. 81% (p = .0180), respectively (Table. Five-year local control, laryngeal preservation, cause-specific survival, and overall survival rates by T stage according to the fifth and sixth editions of the UICC staging system; the number of patients with a tumor with the adjacent sign in parentheses). Factor analysis confirmed the adjacent sign as an independent prognostic factor. The sixth edition of the UICC staging system appears to successfully identify the high-risk group as T3 stage. View Large Image Figure ViewerDownload (PPT)