Between July 1992 and June 1996, 901 new cases of adult acute lymphoblastic leukaemia were recorded in the GIMEMA Archive of Adult Acute Leukaemia; 21 of them (2.3%) had a previous primary malignancy (PM). We found that secondary acute lymphoblastic leukaemia cases (sALL) presented with older age, a high incidence of pre-pre-B immunophenotype and a significantly higher prevalence of cancer among relatives compared to de novo ALL.The leukaemogenic activity of the cytotoxic drugs employed for the treatment of PM may have played a potential role in only a proportion of patients, opening the possibility that some sALL patients may have developed two or more malignancies due to individual predisposing factors.