The aim of this retrospective study was to examine the impact of prolonged chlorambucil (CLB) therapy on the development of second neoplasia (SN) in 389 patients with B-CLL, comparing untreated cases with those receiving CLB as induction plus maintenance therapy. Fifty-nine SN cases were observed (15.1%) at a median follow-up of 79 months. SN occurrence was significantly related to Binet stage. No difference was detected between untreated and CLB treated cases neither in terms of SN incidence (12.2% vs 18.1%) nor in the median follow-up (81 vs 79.1 months). Moreover, SN free survival was not different between these two groups. Four out of 13 CLB treated patients (30.8%) developed s-MDS after a subsequent treatment with fludarabine plus cyclophosphamide (F + C). In conclusion, SN development is dependent on the length of follow-up rather than on therapy duration. F + C should be administered with caution after prolonged CLB therapy.