Inner centromere protein (INCENP) is a member of the Chromosomal Passenger Complex (CPC), which is a four member protein complex essential for proper completion of mitosis and cell division (cytokinesis). Inappropriate chromosomal segregation and cytokinesis due to deregulated expression of chromosome passenger proteins may lead to aneuploidy and cancer including lymphomas. According to our knowledge this is the first study investigating immunohistochemical expression of INCENP in lymphoma cases and cancer tissues in general. Our purpose was to characterize the expression of INCENP in cases of non-Hodgkin B-cell lymphomas, to compare the immunoreactivity between low and high grades and to evaluate the correlation between INCENP and MIB-1 labeling indices. We examined INCENP and MIB-1 immunoreactivity in paraffin sections of 55 samples of non-Hodgkin B-cell lymphomas, obtained from 55 patients, 31 men and 24 women. Thirty were of high grade and 25 were of low grade. Our results showed significantly higher nuclear immunohistochemical expression of INCENP in high grade B-cell lymphomas versus low grade ones. Also INCENP expression was significantly correlated with MIB-1 labeling index. Taken together our results point to a possible association between increased INCENP immunostaining and B-cell lymphoma aggressiveness and also stress the need for further investigating the expression of INCENP and other mitotic regulatory proteins in lymphomas and other malignant neoplasms.