The major fallout of radionuclides from the nuclear power station accident at Chernobyl on 26 April, 1986, occurred in regions of Ukraine and Belarus that are believed to be moderately deficient in dietary iodine. On 17 November, 2000, in conjunction with the Ukraine-Belarus-USA study of developing thyroid disease in a cohort of individuals exposed as children, a workshop was held to review what is known about iodine nutrition in the region, how this might influence the risk of thyroid tumor formation from radioiodine, and whether and how iodine nutrition should be monitored in this long-term project. This report is a summary of the workshop proceedings. Although no precise information about iodine intake in 1986 was found, the prevalence of mild goiter in the region's children suggested iodine deficiency and urinary iodine measurements begun in 1990 indicated that mild to moderate deficiency existed. Increased thyroid iodine uptake and increased thyroid size in 1986 resulting from iodine deficiency would have had counteracting influence on the thyroid radiation dose and knowledge of these parameters is required for dose reconstruction. More problematic is the possible role of iodine deficiency in the years following the accident. Theoretically, the resulting increase in thyroid cellular activity might increase the risk of tumorigenesis but experimental or clinical evidence supporting this hypothesis is meager or absent. Despite this limitation it was considered important to monitor iodine nutrition in the cohort subjects in relation to their place of residence and over time. Methods to accomplish this were discussed.