Significance of positive margins in oral cavity squamous carcinoma. Three hundred ninety-eight consecutive, previously untreated patients undergoing surgery for epidermoid carcinoma of the oral cavity from 1979 to 1983 were reviewed. One hundred twenty-nine patients were classified as having positive surgical margins. Of these, 83 patients had tumor within 0.5 mm of the surgical margin, 9 had premalignant changes at the margin, 9 had in situ carcinoma at the margin, and 28 had invasive cancer at the margin. The remaining 269 patients had uninvolved margins. The significance of positive margins relating to survival, subsequent clinical course, local recurrence, and patterns of treatment failure was examined, along with the impact of adjuvant postoperative radiotherapy on positive margins. The percentage of patients having positive margins progressively increased with increasing T stage: 21% in T1 versus 55% in T4 primary cancer. The overall 5-year survival for patients with negative margins was 60%. For patients with positive margins, 5-year survival was 52%. This difference was statistically significant. The incidence of local recurrence in patients having positive surgical margins was twice as much as in those with negative margins (36% versus 18%). Metastasis rates in the neck and at distant sites were not significantly influenced by the status of the surgical margin. Of the 129 patients with positive margins, 49 received postoperative radiotherapy. In those patients so treated, a trend toward lower recurrence rates was noted. Differences were not statistically significant. This retrospective review confirms the importance of adequate resection of the primary tumor as well as the relative ineffectiveness of adjuvant postoperative radiotherapy in the improvement of local control in patients with positive surgical margins. 