['NAT2, the most important phase II metabolic enzyme for betel quid (BQ), might modify the risk of BQ-related oral and pharyngeal squamous cell carcinoma (OPSCC) in Taiwan.', 'PCR-RFLP and TaqMan assay were conducted for genotyping of NAT2 in 172 OPSCC cases and 170 healthy controls who habitually chewed BQ.', 'The genotypic and allelic type of T341C and C481T in NAT2 are associated with the risk of OPSCC. There were linear trends between increased risk of OPSCC and slowness of NAT2 acetylation haplotypes (P = .017), especially for young subjects (P < .001), light BQ chewers (P = .005), light smokers (P = .023), and alcohol drinkers (P = .001). The interactions on risk of OPSCC were found for NAT2 acetylation haplotypes with status of age, BQ chewing, and alcohol drinking.'] Are nAT2 slow acetylation haplotypes associated with the increased risk of betel quid-related oral and pharyngeal squamous cell carcinoma?