The National Cancer Registry has been operational in the Republic of Belarus since 1973: information on all new cases of malignant tumours is registered. The data are kept in a computer database and used for assessing the oncological status of the population, and for epidemiological studies. We compared findings before the Chernobyl accident of April 26, 1986 (Chernobyl) and findings between 1990 and 2000. The overall comparison on the changes in the incidence of cancer morbidity in Belarus is presented. The increase is statistically significant for all regions, but significantly greater in the most chronically radiation-contaminated region: the Gomel oblast. The paper presents a comparative analysis of the incidence of cancer morbidity in the population of two regions of Belarus, selected for the greatest difference in their radioactive contamination following Chernobyl. The highest contamination occurred in the Gomel region and is mainly due to high levels of radiocaesium (137Cs) in the soil and in the alimentary chain, especially in rural areas. A relatively low radioactive fallout was noticed in the Vitebsk region, considered here as the "control" area. We compare the situation before and after Chernobyl in the two regions. The overall cancer morbidity rate in all organs including colon, urinary bladder and thyroid, was significantly higher in the Gomel region than in Vitebsk. In populations living in two areas with high 137Cs contamination (oblast of Gomel and Mogilev), the peak incidence rates of breast cancer were already reached between the ages of 45-49 years, 15 years earlier than in the Vitebsk region. Belarussian "liquidators" who were mobilised to clean up the most contaminated territory and build the sarcophagus around the destroyed atomic plant, received the highest radiation doses. They had a significant excess of incidence of cancers of colon, urinary bladder, and thyroid gland, when compared with a corresponding adult population of the Vitebsk region. The Relative Risk (RR) of lung cancer among "liquidators" in 1997-2000 significantly exceeded 1, while in the control population it remained stable.