This article describes a validity study conducted among middle school students comparing self-reported sun safety behaviors from a diary with readings from ultraviolet (UV) monitors worn on different body sites. The UV monitors are stickers with panels that turn increasingly darker shades of blue in the presence of increasing amounts of UV light. Three schools participated (N = 527). Statistically significant associations were found between self-reported behaviors and the UV monitor measurements, with Kendall's tau b's ranging from 0.400 to 0.823. Multiple regression was performed and indicator variables created separately for arm (R = .12) and leg (R = .49) coverage by protective clothing. The effect of time spent outdoors on the UV monitor measure was attenuated when the students reported having the corresponding body site covered with clothing. Self-reported shade was not a significant predictor of UV monitor change. Overall, the results provide evidence of validity of students' self-reports of time outdoors and protective clothing use.