Background : In Kauai, Hawaii, we observed an exceedingly high incidence of basal cell carcinoma in an earlier 1-year study. Objective : Our purpose was to report the incidence of basal cell carcinoma in a defined population in Hawaii. Methods : A prospective 5-year population-based incidence study was conducted on Kauai, Hawaii, between 1983 and 1987 to investigate the frequency of basal cell carcinomas in Caucasian residents. A total of 242 residents, 161 men and 81 women, were identified with an initial episode of basal cell carcinoma during the 5-year period. Results : The average annual incidence per 100,000 Kauai Caucasian residents standardized to the 1980 U.S. white population was 576 for men and 298 for women with a combined incidence of 422. The average patient age was 56.5 years, and men had a significantly higher incidence of cancer than women ( p < 0.000001). The head and neck was the most common site. The trunk was the second most common site, representing one third of lesions. Subsequent new basal cell carcinomas occurred in 16.9% of patients. Only 3.3% of patients had recurrent carcinomas after treatment. Conclusion : Kauai's incidence rates of basal cell carcinoma are the highest yet documented in the United States. As an unexpected finding, a decreasing incidence trend was noted in the study's later years and may warrant further investigation. Finally, a significant number of basal cell carcinomas developed on the trunk, suggesting and reinforcing the expectation that sun exposure is not limited to the face and neck in this Hawaiian population.