Ultrasonic aspirators are commonly used to resect brain tumors because they allow safe, rapid and accurate removal of dissected tissue. However, the tissue fragments removed by ultrasonic aspirators are used surprisingly little in daily diagnostics and in clinical research. A comparison between diagnoses made on the tissue fragments removed by the Sonocut ultrasonic aspirator and the tissue in conventional tumor biopsies was made. The correspondence between the amount of Sonocut tissue analyzed and the probability of making the most malignant diagnosis was analyzed statistically in order to limit the amount of tissue fragments, which need to be analyzed, and in order to save tissue for other purposes like molecular genetics and in vitro drug sensitivity assays. Thirty cases were included in the present study and consisted of astrocytomas, glioblastomas, oligodendrogliomas and ependymomas. The results showed that in 8 out of 30 cases only the Sonocut tissue fragments contained the tumor components that provided the most malignant diagnosis. In further 20 cases, the Sonocut tissue fragments and conventional tumor biopsies gave the same diagnoses. In the remaining 2 cases, the most malignant foci were included in the biopsy removed for peroperative frozen section investigation. When the slides with Sonocut tissue fragments were analyzed, the probability of making the most malignant diagnosis increased from 81.3% - 99.1%, when slides from 1 - 5 paraffin blocks were analyzed, respectively. When subgroups of small, medium and big tumors were analyzed, it was found that only 2 paraffin blocks from small tumors need to be prepared to reach 98.3% probability of making the most malignant diagnosis, whereas 5 paraffin blocks from big tumors need to be prepared to reach a 96.8% probability. In conclusion, the study shows that a limited amount of Sonocut ultrasonic tissue fragments improve the diagnostic evaluation of gliomas. These tissue fragments therefore must not be discarded. Only few paraffin blocks need to be prepared to reach close to 100% probability of making the most malignant diagnosis, reducing the amount of slides, which have to be analyzed and saving Sonocut tissue fragments for future use in molecular genetics and drug sensitivity assays.