Sixty-nine intracranial, totally excised meningiomas were immunostained for MIB-1 and p53 protein expression. According to the 1993 WHO criteria, revised by Perry et al., the 69 meningiomas were classified into: grade I = 54 benign meningiomas, grade II = 10 atypical meningiomas, grade III = 5 malignant meningiomas. The patients were followed until death or for an average of 6.7 years. The 69 meningiomas were divided into two groups, according to the absence (n = 42) or presence (n = 27) of recurrences. In the last group we included 3 patients who died of meningioma recurrence. According to the percentage of MIB-1 positively stained cells, meningiomas were divided into three groups: <1% (n = 36), 1-10% (n = 28), >10% (n = 5). We found the MIB-1 labeling index (LI) <1% in 33 grade I (61%) and in 3 grade II (30%) meningiomas. On the other hand, 7 grade II (70%) and all grade III (100%) meningiomas presented a MIB-1 LI >1%. Correlation between histological grade and MIB-1 LI was statistically significant (p = 0.0006). The correlation between MIB-1 LI and follow-up was also highly significant (p < 0.001): the majority of meningiomas which did not recur (32/42 equal to 76%) were characterized by a low (<1%) MIB-1 LI. In the recurrence group MIB-1 LI was significantly higher than in the disease-free patients' group. Moreover, MIB-1 appeared to be a prognostic parameter not strongly related to the histological grade. In fact, it was significantly higher in recurrent histologically benign meningiomas, as compared with benign meningiomas without recurrence (p = 0.0006). Positive p53 protein expression (>1%) was shown in 26/45 meningiomas (57%), with an LI of 1-10% in 18 (40%) and an LI of >10% in 8 (17%) meningiomas. Although the p53 LI tended to be higher in atypical and malignant meningiomas, no significant correlation was found between the p53 expression and the recurrence (p = 0.05). The authors conclude that quantitative MIB-1 labeling is a useful technique in the routine diagnostic assessment of meningiomas, and helpful in obtaining more information about prognosis and thereby in planning the most suitable treatment.