Dividing cells of leaves used as sources of explants from coffee plants (Coffea arabica cv. 'Catimor') and those of their derived calli were analyzed for mitotic aberrations. The studied tissues were prepared by squashing and stained with carbolfuchsin. A total of 1551 leaf and 4568 callus cells were surveyed. The majority (79 %) of leaf and calli (75 %) cells showed normal mitosis, however, cells with mitotic abnormalities were also found in both tissues. These included: polyploids, aneuploids, sticky chromosomes, double prophases and lagging chromosomes. Additionally, interphase cells with micronuclei or binucleated were also observed. The frequencies of these abnormalities were statistically different in calli and leaves. Calli showed a few other abnormalities such as c-mitosis, chained chromosomes, multipolar metaphases and chromosome bridges. Therefore, we conclude that these pre-existing abnormalities originate by errors in the process of normal mitosis in both leaves and in calli, and are therefore not caused by tissue culture conditions. <A NAME="Article"></A>