Specimens of histologically confirmed acoustic neuromas obtained during operation in 25 patients were examined. Quantitative DNA measurements were performed with an image analysis system. From the single cell measurements, the mean DNA content of all tumor cells, 2c deviation index (2c DI), DNA entropy, DNA grade of neoplasia, and percentage of tumor cells with a DNA content of more than 5c (5c exceeding rate) were derived, as well as the mean nuclear area of the tumor cells. Proliferating cell nuclear antigen (PCNA) was identified immunohistochemically. A PCNA score was developed in determining PCNA-positive cells in a total amount of 1,000 cells. Results of quantitative DNA measurements and PCNA scores were compared to clinical symptoms, histology, and time between first onset of symptoms and diagnosis of the tumor. Quantitative DNA measurements revealed the existence of hyperdiploid tumor cells in all neuromas. According to the frequency with which they occurred, tumors could be divided into two categories: 1) tumors with a high percentage of hyperdiploid cells (“hyperdiploid tumors”) and 2) those with a low percentage (“diploid tumors”). Hyperdiploid tumors showed increased values for the 2c DI, mean DNA content, DNA grade of neoplasia, and DNA entropy as signs of increased proliferation. In addition, the PCNA scores were higher in these tumors, indicative of increased DNA synthesis. The mean nuclear area was higher in these tumors. No correlation was found between the results of the DNA analysis and the PCNA score, or the clinical data and the predominant histologic subtype. The results of this study could explain the known differences in growth rate of acoustic neuromas and might also have clinical relevance in identifying patients at high risk for developing tumor recurrences.