BACKGROUND: Colorectal cancer has the highest incidence of all malignant tumours in men and women in Israel. The public was introduced to the concept of screening in the early 1980s, and full programs began in 1983. OBJECTIVES: The study compares patients with colorectal cancer (CRC) who were diagnosed before screening and five years later, for stage differences and survival. METHODS: All patients with CRC who were diagnosed from 1981 to 1982 (period I) and 1986-87 (period II) at Soroka Medical Centre and who were residents of the Negev area were eligible for the study. Data were collected retrospectively from the Israel Cancer Registry and patient files and endoscopic, histological and surgical reports from the Departments of Pathology, Gastroenterology, Oncology and Surgery at Soroka Medical Centre. RESULTS: The study groups included 207 patients with CRC, 85-from period I and 122-from period II. The mean annual incidence of CRC for these 2 periods was 18 and 24.8 cases per 100, 000, respectively, for an increase of 37% (P < 0.001). Five-year-survival in period I was 53.3% and in period II, 39.6% (P = 0.025). Survival did not differ by origin or gender. Dukes' stage, well and moderately differentiated tumours, and left-sided tumours were associated with better prognosis (P = 0.03). Forty-two percent of the cases were less than 64-year-old-at diagnosis, compared with 27% of 2069 Israeli patients in whom CRC was diagnosed in 1991 (P < 0.001). CONCLUSIONS: Before a nation wide decision is made with regard to public screening for CRC with fecal occult blood tests or sigmoidoscopy, the available data should be thoroughly evaluated, and further in-depth investigations performed to determine trends in diagnosis and prognosis.