Prevention of cancer mortality can be achieved by two main routes: (1) detection of precancerous lesions and preventing their progression to cancer, and (2) detecting cancers at an early stage when they are still amenable to curative treatment. Early detection of cancer is dependent on the population being well-informed about cancer, and about how to carry out self-examination as a preliminary screen (followed by a full clinical examination in the event of suspicious symptoms). In this paper the warning signs that the population should be taught to look out for are discussed. Superficial observation and palpation can be used for surface tumours (which comprise 10–15% of the total). A further 60–70% of tumours are of the digestive tract, respiratory tract or urogenital tract. For these, it is argued that a simple occult blood test could be used as a self-administered screening test. Data are presented to show that this is a practicable way for the general population to detect early signs of cancer or pre-cancer, with a high yield of clinically significant results in the occult blood positive persons.