Age, period, and cohort effects obtained from the Poisson age-period-cohort model of NPC in Sihui County, Guangdong Province, South China from 1987 to 2011. A, both males and females shared a similar age-effect pattern. The risk of NPC increased with advancing age up to 50–59 years and decreased at ages >60 years. B, the curves of period effect on the risk of NPC were virtually flat for both sexes. C, the birth cohort curve for males showed that the relative risks of NPC increased from the 1922 cohort to the 1957 cohort and decreased after the 1957 cohort. For females, the relative risks increased with undulation from the 1922 cohort to the 1972 cohort and peaked near the 1972 cohort.