In a prospective study of 93 consecutive untreated patients with B-cell chronic lymphocytic leukemia, we examined the clinical relevance of surface immunoglobulin (sIg) heavy chain (HC) and light chain (LC) isotypes, CD11c or CD25 expression, and the presence of trisomy 12 by fluorescence in situ hybridization (FISH). Careful morphologic evaluation was performed to exclude patients with other forms of chronic lymphoid leukemias, including mantle cell lymphoma, prolymphocytic leukemia, and leukemia phase of lymphoma. In addition, clonally restricted sIg and CD5 surface determinant were expressed in all patients. Clinical presentation, including blood cell counts, clinical stage, and organomegaly, did not correlate with any of the measured variables. After a median follow-up period of 3 years, the particular HC or LC isotype or CD11c expression did not correlate with either disease progression or treatment-free survival. However, trisomy 12 and CD25 expressions were both associated with accelerated disease progression and a shorter treatment-free survival time. Our results confirm the adverse prognostic significance of trisomy 12 expression in chronic lymphocytic leukemia and suggest that CD25 expression may have an unfavorable clinical impact.