BACKGROUND: Lack of cancer incidence information for adolescents and young adults led us to describe incidence trends within the young population of 15 to 49 year-olds in urban Shanghai between 1973 and 2005. METHODS: During 1973 to 2005, data on 43,009 (45.8%) male and 50,828 (54.2%) female cancer cases aged 15-49 years from the Shanghai Cancer Registry were analyzed. Five-year age-specific rates, world age-standardized rates, percent change (PC), and annual percent change (APC) were calculated using annual data on population size and its estimated age structure. RESULTS: During the 33-year study period, overall cancer incidence of adolescents and young adults among males marginally decreased by 0.5% per year (P<0.05). However, overall cancer incidence for females slightly increased by 0.8% per year (P<0.05). The leading cancer for males in rank were liver, stomach, lung, colorectal, and nasopharyngeal cancers and for females were breast, stomach, colorectal, thyroid, and ovarian cancers. Among specific sites, incidence rates significantly decreased for cancers of the esophagus, stomach, and liver in both sexes. In contrast, incidence rates significantly increased for kidney cancers, non-Hodgkin lymphoma, and brain and nervous system tumors in both sexes and increased for breast and ovarian cancers among females. CONCLUSIONS: Overall cancer incidence rates of adolescents and young adults decreased in males whereas they increased in females. Our findings suggest the importance of further epidemiology and etiologic studies to further elucidate factors contributing to the cancer incidence trends of adolescents and young adults in China.