The purpose of this study was to examine the relationship between physical activity (PA) and body mass index (BMI) in young women. Eighty-seven young adult women (age: 20.8 ± 1.6 years; BMI: 22.7 ± 2.9 kg/m2; 77% Caucasian) participated in this cross-sectional, descriptive study conducted at a large university in the south central United States. Participants simultaneously wore an accelerometer and an unsealed pedometer at their waist for 7 consecutive days. At the end of the week they completed The International Physical Activity Questionnaire (IPAQ) short-form to obtain self-reported PA during the same week that the accelerometer and pedometer were worn. Correlation coefficients were calculated for all PA variables and BMI. Data from the accelerometers and pedometers indicated the women in this study accumulated 31.7 ± 12.6 minutes of moderate PA, 5.1 ± 6.7 minutes of vigorous PA, and 7,821.3 ± 2,487.7 steps per day. All of the correlation coefficients between the PA variables and BMI were small. Interestingly, the only statistically significant correlation was between BMI and self-reported vigorous PA (r = -0.22, p = 0.03). Time spent in vigorous (r = -0.11, p = 0.31) and moderate (r = 0.19, p = 0.07) PA from the accelerometer, as well as steps per day from the pedometer (r = -0.04, p = 0.70), were not significantly correlated with BMI. In addition, self-reported moderate PA (r = -0.08, p = 0.47) did not share a notable relationship with BMI. In this study of young adult women, the correlations between PA and BMI were small and only self-reported vigorous PA exhibited a statistically significant relationship with BMI. Future studies should include a larger, more heterogeneous sample of participants to further explore the relationship between PA and BMI in young adult women. Keyword(s): health promotion, physical activity