INTRODUCTION:Chronic lymphocytic leukemia (CLL) is a disorder of mature but dysfunctional monoclonal B cells. Microenvironment, antigenic stimulation and genetical mutations are demonstrated in etiopathogenesis. We aimed to evaluate the expression of CD11c in patients with CLL and its possible clinical significance. METHODS:Data of 259 patients with CLL between 2010 and 2016 in Trakya University Faculty of Medicine, including age at diagnosis, sex, whole blood count, stage, percentage of CLL cells in bone marrow, line of treatments, development of Richter's transformation and secondary tumors, autoimmune complications, IgG level, prognostic cytogenetic analysis, and length of survival were recorded from files. RESULTS:151 patients were male (58.3%) and 108 were male (41.7%). Mean age was 70 (21-92) years. CD11c was observed to be positive (>%20) in 103 patients (39.8%). Development of Richter's transformation, secondary tumors and ITP was significantly frequent in patients with CD11c positivity (P values .000, .003, .000 respectively). Also, IgG levels were significantly lower in this group (P = .000). Hemoglobin level, RAI stage and bone marrow CLL infiltration percentage were statistically related with CD11c (P values .036, .037, .000 respectively). Finally, CD11c was statistically related (in positive group 70 months, negative group 79 months, P = .001). CONCLUSION:CD11c, expressed not only in Hairy cell leukemia but also in dendritic cells, macrophages and monocytes is a differentiation marker for inflammation. Prolonged inflammation in the microenvironment of CLL cells may cause a susceptibility to autoimmune disorders and secondary tumors in CLL, in this way, an increase in mortality.