Chordoma shows various degrees of atypia histologically, however, the relationship between the histological features and the biological behavior still remains controversial. The authors subclassified 17 specimens with chordoma into two groups (ie, trabecular type showing a trabecular patterns and solid type mainly consisting of a diffuse proliferation of tumor cells). The histological grading was performed according to the degree of nuclear atypia on a scale of 1 to 3. Using DNA flow cytometric and immunohistochemical techniques, both the proliferative index (% S + G2 + M phase) and the MIB-1 labeling index (LI) of the tumor cells were estimated regarding their proliferative activities. In addition, p53 overexpression was also investigated using immunohistochemical techniques. There were eight (47.1%) specimens of trabecular type and nine (52.9%) of solid type. In nine specimens of solid type, those with higher nuclear atypia (grade 2 or 3) were significantly more frequent (five specimens, 55.6%) than in trabecular type in which all of the eight specimens were grade 1 (P = 0.44). The proliferative index was significantly higher in grade 2 or 3 lesions than in grade 1 lesions (P = .014), and the MIB-1 LI tended to be higher in solid type than in trabecular (P = .088). p53 overexpression was detected in two specimens of solid type, and the MIB-1 LI in these two specimens was significantly higher (P = .037) than that in the specimens without p53 overexpression. It was considered that the preceding anaplastic histological features, including either diffuse proliferation or high grade nuclear atypia, together with p53 overexpression, were thus closely related to the proliferative activities in chordomas.