Relationship between histologic features, DNA flow cytometry, and clinical behavior of squamous cell carcinomas of the larynx. Flow cytometric analysis of DNA content was done on 133 primary squamous cell carcinomas of the larynx. Overall, 76 tumors (57.1%) were not diploid (aneuploid or tetraploid). The DNA index (DI) was calculated and grouped into three levels. Fifty-seven cases had a DI in a range of 1.85 to 2.15 (44 diploid and 13 tetraploid). The cases were grouped in relation to ploidy, proliferative index, and the tumor-node-metastasis (TNM) system. Every group was analyzed with respect to survival rate. Ploidy was related to histocytologic grade. In well-differentiated tumors (G1) survival rates at 48 months were 41.7% in diploid cases and 27.7% in nondiploid ones (relative risk [RR], 2.01; 95% confidence interval [CI], 0.89, 4.52). In NO cases that underwent surgery, survival rates at 48 months were, respectively, 81.8% and 49.2% (RR, 5.07; 95% CI, 0.76, 33.93). These results suggest that ploidy may be a new independent parameter of prognosis in squamous cell carcinoma of the larynx. This is useful in clinical practice because it allows the clinician to recognize those cases with poorer prognosis among the early tumors at a stage where other prognostic parameters are not yet available. 