The purpose of this study was to explore the relationship between health-related fitness knowledge (HRFK) and various intensity and activity levels of physical activity in male and female high school students. At the end of a Fitness for Life course, high school students (N = 280) completed a HRFK questionnaire and the Leisure-Time Physical Activity Questionnaire (Godin & Shephard, 1985). Pearson correlations were computed among physical activity levels (mild, moderate, and strenuous). A one-way MANOVA with appropriate follow-up univariate ANOVAs examined the effect of gender on physical activity intensity scores (total, healthy, and strenuous). A one-way ANOVA examined the difference in HRFK scores between the active group and the less active group. Results showed no significant correlation between HRFK and all physical activity scores. Females had higher HRFK scores and males had higher physical activity scores for all intensity levels. Ninety-two percent of all students were classified as active and males were more active than females. There was no significant difference in HRFK scores between the active group and the less active groups.