Supplementary prognostic factors should be added to the TNM classification for oral squamous cell carcinomas in order to optimize its clinical value. We have recently published two prognostically valuable malignancy grading systems based on histopathology and immunohistology of the most invasive cells in oral squamous cell carcinomas (OSCCs). However, a major problem with classifications based on histologic features is frequent lack of interobserver agreement which limits the clinical value of subjective histologic classifications. Thirty-eight file cases of OSCCs were therefore graded by three pathologists according to criteria of the histologic malignancy grading system which includes 5 morphologic features, each graded from 1 to 4. Agreement was calculated by kappa statistics, which showed that interobserver agreement was not optimal, but significantly better than by chance alone. We also studied the reproducibility of grading of immunohistologic membrane expression of a tumor-associated marker (blood group antigen H), and found a similar level of agreement. We conclude that the clinical value of our grading systems will increase by improving reproducibility.