Loss of the Y chromosome in meningiomas from 17 male patients was examined by cytogenetic analysis and by Southern blot hybridization with a series of Y-specific DNA probes. Cytogenetic analysis revealed loss of the Y chromosome in seven of 17 (41%) of the tumors whereas Southern blot hybridization showed loss of Y-associated sequences in only three of 17 (18%). Although the incidence of Y-chromosome loss was less by Southern blot hybridization than by cytogenetic analysis, the finding that loss of Y is present in the original uncultured tumor specimen suggests that a gene or genes on the Y chromosome may play a role in growth control of meningioma cells, and loss of this gene may be associated with tumor progression. The difference in the incidence of Y loss between the two methods indicates that both methods should be used when examining chromosome losses.