Objective: The researchers assessed the effectiveness of a pedometer intervention and differences in walking behaviors according to body mass index (BMI). Participants: Two hundred ninety college students completed the intervention from January to February 2005. Methods: Participants wore pedometers 5 days per week for 12 weeks and completed questionnaires assessing demographic information. The authors calculated daily step averages for weeks 1, 6, and 12. They then classified students as underweight (UW), normal weight (NW), or overweight/obese, by BMI. The authors analyzed data using repeated-measures analysis of variance. Results: The average number of daily steps increased from week 1 to week 6 (p less than 0.001) and week 12 (p = 0.002). UW participants reported the fewest steps at each time point, but the difference was significant only when compared with NW participants (p = 0.03). Conclusions: These results support the effectiveness of a pedometer intervention to increase walking in college students. Health benefits other than weight management should be emphasized to maximize the effects for all students. (Contains 2 figures.)