Abnormal expression of the retinoblastoma protein (pRb) and cyclin D1 have been reported in a variety of malignancies, but the frequencies of these deregulations and their relation to prognosis in colorectal cancer has not been clarified. We characterised 90 colorectal cancers with respect to immunohistochemical expression of cyclin D1, pRb and Ki-67. Two of 90 (2%) tumours lacked nuclear pRb staining, indicating inactivation of the protein, while 10 (11%) expressed high levels of pRb. Abnormal expression of pRb was significantly correlated to low levels of nuclear cyclin D1 observed in 32% of the tumours. Strong nuclear cyclin D1 expression was detected in 12% of the tumours. Cytoplasmic staining of cyclin D1 was observed in 17% of the tumours, showing an inverse relationship (P = 0.006) to the Ki-67 labelling index. Eight of 11 tumours with high nuclear overexpression of cyclin D1 and both tumours with pRb defects were located in the right colon in comparison with zero of 25 in the rectum (P = 0.009). Regarding prognosis, neither pRb nor cyclin D1 expression correlated with patient survival.