Thailand is one of the few developing countries for which population-based cancer survival data are available. Using clinical follow-up information and reply-paid postal enquiries, 10,333 residents of Khon Kaen province registered with cancer in the period 1985-1992 were followed-up to the end of 1993. The sites of the most common cancers in the province were liver (5-year relative survival rate 9.2%), cervix (60.1%), lung (15.4%), breast (48.1%) and large bowel (41.9%). Results for Khon Kaen were compared with age-standardized survival data for the US and Scotland. Survival was consistently higher for US whites compared to Khon Kaen residents for those cancers whose prognosis is associated with early diagnosis (breast, cervix and large bowel) or the availability of intensive therapy (leukaemia and lymphoma). The main implication of these results for cancer control in Thailand is that the interventions of greatest potential benefit are those designed to promote early detection. More than one-third of all cancers in Thailand are liver tumours: primary prevention through control of hepatitis-B infection and liver fluke infestation is the only effective strategy for their control.