Immunohistochemistry has revolutionized the diagnosis, treatment and management of B-cell Non-Hodgkin's lymphomas (NHL). Proliferation of tumour cells can be used to demonstrate the progression of these malignancies. Immunohistochemically an evaluation can be made using the nuclear antigen Ki-67. This study's objective was to determine the proliferation index (PI) of Ki-67 of B-cell NHLs. This was a cross section study conducted to evaluate 28 B-cell NHLs at the University Teaching Hospital Histopathology laboratory between November 2013 and April 2014. Tissues were cut for immunohistochemical analysis using a microtome. The monoclonal antibody Ki-67 used in the study was from Dako, Glostrup, Denmark. The Labelled Streptavidin Binding (LSAB) staining was used to amplify and view the reaction. The intensity of the reaction was quantified by taking into account the percentage of tumour cells manifesting nuclear colour reactions. Data was analysed using SPSS version 16.0 software for windows; Univariate analysis of the antibody profile was conducted to determine the distribution patterns of the B-cell NHLs. Fisher's exact test with a P-value of less than 0.05 was considered statistically significant. Of all the 28 cases of B-cell Non-Hodgkin's lymphomas in the study 82.1% (23 cases) expressed the Ki-67 antigen with a mean expression percentage of 46.3%. All the Burkitt lymphoma cases (5/5) were positive for the Ki-67 antigen and had the highest values all of which were above 85%. The rest of the subtypes showed variable expression percentages for the Ki-67 antigen. The results reveal that most cases of B-cell Non-Hodgkin's lymphomas express the Ki-67 antigen. The expression intensity of the majority is highly suggestive of aggressive nature of the B-cell Non-Hodgkin's lymphomas irrespective of the subtype. Hence there is need for more aggressive clinical management of the tumour.