A decline of oropharyngeal cancer has already been predicted for Thailand since the early 1960s. To substantiate these predictions it was the purpose of this study to examine trends in the incidence of oropharyngeal cancer in the province of Chiangmai, (1988-1999). Data on cancer incidence were extracted from the annual reports of the Cancer Registry, Cancer Unit, Faculty of Medicine, Chiangmai University, Thailand (1992-1999) and an IARC report on cancer in Thailand (1988-1991). The age-standardized annual incidence per 100000 of oral cancer in males dropped from 3.6 (1988-1991) to 1.2 in 1999 (P for trend 0.0002) and in females from 2.6 (1988-1991) to 1.1 in 1999 (P for trend 0.007). Similar trends in males and females for cancer of the tongue, oropharynx and hypopharynx were seen. The age-standardized annual incidence for cancer of the lip, salivary gland and nasopharyngeal carcinoma remained unchanged. Changes of traditional oral habits such as betel quid chewing and smoking of traditional cigars seem to have resulted in a marked decrease of oral cancer in both men and women in the recent past.