A review is presented of the major cancer surveys conducted in trans-Saharan Africa since the end of the First World War, starting with the more numerous relative ratio or frequency studies before proceeding to the four recent incidence rate surveys which have taken place in Johannesburg, Kivu and Ruanda Urundi, Kampala, and Lourenco Marques. An account is then given of the three years cancer incidence rate survey in Ibadan, Nigeria, which extended from April 1960 until the end of March 1963. In describing the organisation and running of the Ibadan survey particular attention is paid to a number of sociological studies designed to elucidate special local circumstances which might be affecting the validity of the eventual results. One of these subsidiary surveys was concerned with the attitude of the population towards modern medical facilities and the extent of their continued reliance upon traditional modes of treatment. Studies of prominent local tumours made in the course of the main survey also receive individual mention. Among them was an attempt to assess the prevalence of Kaposi's Sarcome throughout Nigeria, an exercise which served to demonstrate the complexities of epidemiology in such a setting. The incidence rate survey in the town of Ibadan showed low crude annual rates of approximately 45 per 100:000 of the population for all cancers in both sexes. However, during much of their life span Ibadan people seem to have age specific cancer incidence rates which are only slightly lower than those of the U.S.A., with the notable exceptions of the 5 - 9 age group and the over-fifties. Young male children have a very high incidence of the Burkitt Tumour, making the overall rates for this age much higher than those in the United States whilst in older people in Ibadan the cancer incidence rate, which had been rising with age, falls off steeply. Apart from the Burkitt Tumour and tumours of the reticulo-endothelial system generally, the striking feature of the Ibadan cancer scene is the high incidence of primary liver celled carcinoma among males. Finally, attention is drawn to the unsatisfactory nature of relative ratio surveys in a continent with rapidly developing medical services and suggestions are made regardint the interpretation of some of the Ibadan incidence survey results. It is emphasised that caution must still be exercised even when considering cancer incidence rates if these have been based entirely upon hospital diagnosed cases, drawn from a population whose ages are not accurately known and whose elderly members may be disinclined to come to hospital.