In this review of 105 consecutive patients who underwent operation for previously untreated, N0 squamous carcinomas arising in the oral tongue or the floor of the mouth, 86 percent of the determinate patients remained alive and well 2 years after treatment. Included were 48 patients, 49 patients, and 8 patients who had T1, T2, and T3 tumors respectively. Elective cervical lymphadenectomy was performed in about a third, but tumor staging did not facilitate selection of those who were most likely to have occult metastases. For this reason, we retrospectively assessed the impact of tumor thickness using an optical micrometer to measure the thickness in millimeters of the excised tumors in routinely prepared paraffin sections. Disease-related death appears to be unusual when oral tumors are thin (2 mm or less), regardless of the tumor stage. Multivariate analysis confirms that increasing tumor thickness, rather than tumor stage, had the best correlation with treatment failure and survival. These findings need to be verified in prospective studies involving a larger patient population and other head and neck sites, but they strongly suggest that measurement of tumor thickness may be a better way to select those oral cancer patients who are most likely to benefit from elective treatment of the N0 neck.