Abstract: This study is aimed at finding out whether or not activation of the coagulation system and fibrin deposition occurs in Chronic Myeloid Leukaemia (CML) patients with Hyperleucocytic Syndromes (HLS). A total of 14 CML patients with HLS were evaluated with respect to white cell count, presence of symptoms and signs of HLS and plasma D-dimer levels. Equal number of sex and age matched CML patients without HLS were similarly evaluated. Patients with HLS had a significantly (p<0.05) higher mean white cell count of 510x109 L-1 as compared to their counterparts who did not present with HLS and had a mean white cell count of 120x109 L-1. All CML patients without HLS had normal levels of D-dimer with a mean value of 87 ng mL-1. However, among the CML patients with HLS, 78.6% had elevated D-dimer levels with a mean value of 325 ng m L-1, while the remaining 21.4% had normal D-dimer levels with a mean value of 95 ng m L-1. This data was interpreted to indicate that in the majority of cases of CML with HLS, microvascular endothelial damage and fibrin deposition occur and contribute to the microvascular blockade initiated by leucostasis. There is therefore, the need to investigate a possible beneficial role of low dose anticoagulation in mitigating secondary fibrin deposition and minimizing tissue infarction and sensory organ damage in such patients.