We present cytogenetic findings in 9 patients with Alzheimer's disease (AD) and 35 normal age matched controls. The study was undertaken due to reports of increased aneuploidy in individuals with AD. Coded peripheral blood chromosome preparations were evaluated for aneuploidy; there were 4.5% hypomodal cells in AD patients compared with 5.5% in controls. There were no hypermodal cells in the AD group and only 0.7% among the controls. Statistical analyses of the results did not show any differences between AD patients and controls in these data. There was a statistically significant increase in the loss of C group chromosomes in the old controls which we attribute to ageing.