This study was carried out to determine the occurrence, prevalence and contributing factors to the incidence of goitre in Yewa north local government area of Ogun state, southwestern Nigeria. To achieve these objectives, soil, water, and cassava tubers were collected from four villages -- Igbogila, Egua, Sawonjo and Imoto and from Lagos (about 250 m to the ocean) as a reference location, in order to determine their iodine concentrations. The results of the analyses indicated a soil mean iodine range of 2.1-5.8 microg g(-1); a cassava mean iodine value of 2.3-3.5 mug g(-1) and a drinking water mean iodine value of generally <1.0 microg L(-1) in all the four villages. These values of iodine in soil and water of the four villages are considered low when compared with the soil iodine value of 7.4 microg g(-1) and water iodine value of 6.1 microg L(-1) obtained from Lagos. The limestone unit of the study area remains an inhibiting factor in the bioavailability of the iodine because of its alkalinity. Statistical analysis has shown that there was significant difference between iodine concentration in the soils and the drinking water, and a correlation between the soil iodine and organic matter content at p < 0.05. The correlation between soil iodine and granulometric fractions occurred at p < 0.01. Potential goitrogens in the commonly consumed cassava products might also have contributed to the prevalence of goitre in the study area. Both the females and the adults (i.e., less mobile groups) were found to be vulnerable to goitre development in these villages.