Context: The incidence of nonmelanoma skin cancer is increasing rapidly among elderly persons, but little is known about its incidence in the population younger than 40 years. Objectives: To estimate the sex-and age-specific incidences of basal cell carcinoma and squamous cell carcinoma in persons younger than 40 years in Olmsted County, Minnesota, and to evaluate change in incidence over time; to describe the clinical presentation, rate of recurrence and metastasis, and histologic characteristics of these tumors in this population-based sample. Design: Population-based retrospective incidence case review. Setting: Residents of Olmsted County, Minnesota, a population with comprehensive medical records captured through the Rochester Epidemiology Project. Participants: Patients younger than 40 years with basal cell carcinoma or squamous cell carcinoma diagnosed between 1976 and 2003. Main Outcome Measures: Incident basal cell carcinomas and squamous cell carcinomas and change in incidence of these tumors over time. Results: During the study period, 451 incident basal cell carcinomas were diagnosed in 417 patients and 70 incident squamous cell carcinomas were diagnosed in 68 patients. Of these tumors, 328 were histologically confirmed basal cell carcinomas and 51 were histologically confirmed squamous cell carcinomas. Overall, the age adjusted incidence of basal cell carcinoma per 100 000 persons was 25.9 (95%confidence interval [CI], 22.6-29.2) for women and 20.9 (95%CI, 17.8-23.9) for men. The incidence of basal cell carcinoma increased significantly during the study period among women (P<.001) but not men (P=.19). Nodular basal cell carcinoma was the most common histologic subtype; 43.0%of tumors were solely nodular basal cell carcinoma and 11.0%had a mixed composition, including the nodular subtype. The incidence of squamous cell carcinoma was similar in men and women, with an average age-and sex-adjusted incidence per 100 000 persons of 3.9 (95%/ CI, 3.0-4.8); the incidence of squamous cell carcinoma increased significantly over the study period among both women (P=.01) and men (P=.04). Conclusions: This populationbased study demonstrated an increase in the incidence of nonmelanoma skin cancer among young women and men residing in Olmsted County, Minnesota. There was a disproportionate increase in basal cell carcinoma in young women. This increase may lead to an exponential increase in the overall occurrence of nonmelanoma skin cancers over time as this population ages, which emphasizes the need to focus on skin cancer prevention in young adults. Context: The incidence of nonmelanoma skin cancer is increasing rapidly amongderly persons, but little is known about its incidence in the population younger than 40 years. Objectives: To estimate the sex-and age-specific incidences of basal cell carcinoma and squamous cell carcinoma in adults younger than 40 years in Olmsted County, Minnesota, and to evaluate change in incidence over time; to describe the clinical presentation, rate of recurrence and metastasis, and histologic characteristics of these tumors in this population-based sample. Design: Population- Based retrospective incidence case review. Setting: Residents of Olmsted County, Minnesota, a population with comprehensive medical records captured through the Rochester Epidemiology Project. Participants: Patients younger than 40 years with basal cell carcinoma or squamous cell carcinoma diagnosed between 1976 and 2003. Main Outcome Measures: Incident basal cell carcinomas and squamous cell carcinomas and change in incidenc Of these tumors over time. Results: During the study period, 451 incident basal cell carcinomas were diagnosed in 417 patients and 70 incident squamous cell carcinomas were diagnosed in 68 patients. Of these tumors, 328 were histologically confirmed basal cell carcinomas and 51 were Overall, the age adjusted incidence of basal cell carcinoma per 100 000 persons was 25.9 (95% confidence interval [CI], 22.6-29.2) for women and 20.9 (95% CI, 17.8-23.9) for men . The incidence of basal cell carcinoma increased significantly during the study period among women (P <.001) but not men (P = .19). Nodular basal cell carcinoma was the most common histologic subtype; 43.0% of tumors were solely nodular basal cell carcinoma and 11.0% had a mixed composition, including the nodular subtype. The incidence of squamous cell carcinoma was similar in men and women, with an average age-and sex-adjusted incidence per 100 000 persons of 3.9 (95% / CI, 3.0-4.8);incidence of squamous cell carcinoma significantly significantly over the study period among both women (P = .01) and men (P = .04). Conclusions: This populationbased study demonstrated an increase in the incidence of nonmelanoma skin cancer among young women and men residing There was a disproportionate increase in the overall occurrence of nonmelanoma skin cancers over time as this population ages, which emphasizes the need to focus on skin cancer prevention in young adults.