School sexual harassment (SH) is defined as unwelcome behavior of a sexual nature that interferes with a student's ability to learn. There is an important need for schools to assess the prevalence of SH and its relation to school climate to guide intervention efforts. This study investigated 3 research questions: (a) Is there psychometric support for a 4-item multilevel measure of SH? (b) What is the prevalence of SH in a statewide high school sample, and how does SH vary across gender, grade level, race-ethnicity, and socioeconomic status? (c) Is an authoritative school climate--characterized by strict but fair discipline and supportive teacher-student relationships--associated with lower levels of SH for students? A statewide sample of high school students (N = 62,679) completed a school climate survey that included a new 4-item measure of SH. Results of a multilevel confirmatory factor analysis indicated good fit for a single SH factor at both student and school levels. A multiway analysis of variance demonstrated the high prevalence of SH and variations across demographic groups. Multilevel hierarchical regression analyses indicated that an authoritative school climate accounted for 5.7% of the student-level variance and 38.3% of the school-level variance in SH scores. Routine assessment of SH can help school psychologists bring attention to this underrecognized problem.