The chromosomes of 7 neurinomas and one neurosarcoma were studied. Three of the neurinomas had a normal, diploid stemline but the other four tumours had pseudodiploid‐hypodiploid stemlines. In the latter stemlines the chromosomal abnormalities were restricted to the groups B, C, E17–18 and G. The three, first mentioned chromosome groups also appeared to participate in the formation of markers, which were found in 3 of the 4 abnormal stemlines. The numerical and structural pattern in the neurinomas differed from that observed both in the meningomas and in the pituitary adenomas. The neurosarcoma had a hypertriploid mode, and the cells in the modal region usually had 12–14 markers. Due to the extensive chromosomal rearrangements in the sarcoma cells it was only possible to find a few karyological similarities between the neurosarcoma and the neuri