One hundred fifty-two unselected, consecutive patients with T1-2N0 laryngeal squamous cell carcinoma received radical radiation therapy at the Division of Radiotherapy, Centro di Riferimento Oncologico, Aviano, Italy. Thirty-one (20.4%) of the patients showed disease recurrence or persistence (R/P) after radiotherapy. Flow-cytometric DNA ploidy measurements were performed in 72 cases; 20 had tumor R/P and 52 did not. Tumor R/P occurred more frequently (in 17 [85%] of 20 cases) in patients with diploid tumors. The hazard ratio of recurrence in diploid tumors as compared with aneuploid tumors, after inclusion of all the other significant prognostic factors in a Cox proportional hazards model, was 8.9 (P < .01). Therefore DNA ploidy seems to be an important marker of tumor R/P in patients with T1-2N0 laryngeal carcinoma after radiotherapy.