Episodic acute overexposure to ultraviolet (UV) radiation (i.e., sunburn) is an important risk factor for two types of skin cancer: basal cell carcinoma and melanoma. Melanoma is the most lethal type of skin cancer. In 2003, a total of 45,625 new cases of melanoma were diagnosed in the United States, and 7,818 persons died from the disease. A meta-analysis of 57 studies indicated that the relative risk for melanoma among persons with sunburn history compared with those without sunburn history was 2.03 (95% confidence interval [CI] = 1.73-2.37). Monitoring sunburn prevalence with population-based surveys allows an estimate of compliance with sun-protection behaviors, assessments of risk for developing skin cancer, and measurement of the success of prevention programs. To evaluate trends in sunburn prevalence among U.S. adults, CDC analyzed cross-sectional data from the 1999, 2003, and 2004 Behavioral Risk Factor Surveillance System (BRFSS) surveys. This report describes the results of that analysis, which indicated that sunburn prevalence among all adults increased from 31.8% in 1999 to 33.7% in 2004. Further research is needed to determine which interventions will best improve sun-protection behaviors among the public.