Computer-based sun safety instruction has many advantages that may be attractive to health educators in schools. An educational multimedia computer program on sun safety was produced on CD-ROM for children in grades 4 and 5, which was based on the "Sunny Days, Healthy Ways" sun safety curriculum (SDHW). Its effects on children's sun safety knowledge, attitudes and behaviour were evaluated with 162 students in 8 fourth and fifth grade classes in a randomized pretest-posttest 2 x 2 factorial design. Children interacting with the CD-ROM program showed significant improvements in knowledge (p = 0.007). The effect on knowledge may have indirectly improved children's sun protection (r = 0.201, p = 0.013), even though the CD-ROM program did not directly increase sun protection (p > .05) or improve attitudes (p > .05). The CD-ROM program may be a cost-effective and administratively acceptable sun safety instructional strategy, however, like many short prevention strategies, it will be most successful at conveying information on sun safety to children.