Two sisters, 11 and 9 years old respectively, had the clinical features of a progressive neurological disorder similar to the ataxia-telangiectasia (AT) syndrome. The two patients have ataxia and chromosome instability with rearrangements of chromosomes 7 and 14 but no telangiectasia, nor the range of immunological anomalies typical of AT. Comparison with similar cases from the literature leads to the conclusion that either there is a specific disorder characterized by ataxia-without-telangiectasia and with the same cytogenetic pattern of AT, or AT shows a wider variability of phenotypic expression than thought before.