Although some studies have examined the expression of aberrant markers such as CD2, CD7, CD10, CD13, CD33, and CD34 on B cells in chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), a uniform multiparametric analysis of the frequency of expression of these markers using stringent criteria is lacking. By using 3-color flow cytometry, we analyzed 117 cases (bone marrow, 71; blood, 31; lymph nodes, 15) for coexpression of aberrant markers with CD19. Marker expression was considered positive when present on at least 20% of CD19+ cells. Of 117 cases, 40 (34.2%) showed expression of 1 or more aberrant markers. Expression of 4 aberrant markers was seen in 1 case, 3 in 4 cases, 2 in 15 cases, and 1 in 20 cases. Kaplan-Meier survival curves and the log-rank test revealed that the group with aberrant markers showed significantly shortened overall survival compared with the group without aberrant markers (P < .001). There is considerable phenotypic heterogeneity in CLL/SLL, and expression of aberrant markers indicates aggressiveness.