Skin cancer is increasing, and prevention programs are essential. This study evaluated the impact of a skin cancer prevention program on sun-protection habits and swimming pool environments. The intervention included staff training; sun-safety lessons; interactive activities; providing sunscreen, shade, and signage; and promoting sun-safe environments. A randomized trial at 28 swimming pools in Hawaii and Massachusetts tested the efficacy of this program (Pool Cool) compared with an attention-matched injury-prevention control program. Results showed significant positive changes in children's use of sunscreen and shade, overall sun-protection habits, and number of sunburns and improvements in parents' hat use, sun-protection habits, and reported sun-protection policies and environments. Observations corroborated the positive findings. Pool Cool had significant positive effects at swimming pools in diverse audiences.