Fifty-three patients affected with B-cell chronic lymphocytic leukemia (CLL) younger than 50 years and observed in two hematological institutions have been retrospectively evaluated in order to verify whether this disease has different clinico-hematological features at presentation and different prognosis as compared to older cases. In our experience young cases with B-CLL diagnosis, confirmed by immunophenotype in 90.5% of patients, accounted for 7.1% of the whole CLL population. Sex distribution, mean peripheral lymphocyte count, platelet count, distribution among Rai's and Binet's stages, total tumor mass (TTM) score, histological pattern of bone marrow infiltration and lymphocyte doubling time (LDT) were similar to a series of 201 CLL cases older than 50 years. Only hemoglobin mean level was significantly higher in younger patients (13.1 +/- 2.1 vs 12.2 +/- 2.6 g/dl; p < 0.01). The overall median survival was 7.1 years. Rai and Binet staging classifications and TTM score system retained their prognostic value in this CLL population. In addition, cases fulfilling criteria of "smoldering" CLL, had a very long survival (75% survival probability at 16 years). Life-expectancy of younger patients was significantly longer than that of older ones (median survival, 7.1 versus 4.1 years; p < 0.05). However, when the background mortality due to non-CLL related deaths (i.e., cardiovascular complications, epithelial cancers) was removed, survival advantage of young cases disappeared. In conclusion this study confirms that prognosis of young CLL patients can be easily assessed using the current well-defined criteria. Since age is not by itself a criterion for intensifying treatment, further efforts to identify those young CLL patients who qualify for more aggressive therapy should be made.