Data collected by the population-based Singapore Cancer Registry show rapidly increasing incidence for both cancer of the colon (annual average of 3-6%) and rectum (annual average of 3-5%) over the period 1968 to 1982. The cancer incidence rates were generally highest among the Chinese in whom the latest age-adjusted rates (1978-82) for colon were 14.3 per 100,000 in males and 14.9 in females, and for rectum 12.5 in males and 10.0 in females. The rates were intermediate for Indians and lowest in Malays. In both sexes, foreign-born Singapore Chinese (mostly born in China) had significantly lower risks for colon cancer compared to local-born Chinese (RR 0.71 in males, RR 0.72 in females, both p less than 0.05). There were no discernible differences between the two groups for rectal cancer. Internationally, Singapore's incidence rates for both sites rank roughly midway between the lows of Asia and Eastern Europe and the highs of Western Europe, North America and New Zealand. Among Chinese populations worldwide, the Singapore rates are also intermediate between the low rates in Shanghai and the high rates in Hawaii and California. The rates among Singapore Indians are generally higher than those in Bombay, Madras and Bangalore. These findings strongly suggest the importance of environmental lifestyle related risk factors among which, on current knowledge, dietary intakes feature prominently. The per capita food availability in Singapore especially in meat and animal fat, has also increased markedly over the last two decades.(ABSTRACT TRUNCATED AT 250 WORDS)