A total of 54,361 students in seventh through twelfth grades completed a survey examining the impact of perceived harm of marijuana use, ease of access in obtaining marijuana, and perceived parent/peer disapproval of marijuana use on youth involvement in annual and recent marijuana use. Results indicated that 1 in 6 (16 percent) students used marijuana in the past year, while 1 in 10 (10 percent) used marijuana in the past month. Students at highest risk for marijuana use were those who felt use was not harmful/somewhat harmful, felt it was easy/very easy to access marijuana, and had parents/peers who did not disapprove of use. Findings can assist prevention specialists to more thoroughly understand how perceived harm, ease of access, and parent/peer disapproval affect marijuana use among youth. Consistent parent-child communication on marijuana use should be encouraged. (Published Abstract)