College-student weight gain has been well-documented. However, little is known about the sex differences in weight gain and related behaviors during the transition to college. A repeated-measure study design was used to reveal measured weight changes from October to December 2005 among male and female college students. Three-hundred seventy-nine college students (60% males) participated in both weight assessments and revealed weight gains occurring early in college. Weight gains were found to be of greater incidence and magnitude among college males in the study. More than 25% of both college males and females gained >2.3 kg body weight in an 8-week period. Females starting the study with overweight and obese body mass index (calculated as kg/m(2)) scores were less likely to gain than either obese or overweight body mass index males or low to healthy body mass index students of both sexes. A life-course perspective was used to analyze focus group discussions conducted among students who participated in the weight assessments and explored their perceptions of the transition in eating and exercise behaviors when coming to college. Students described struggles in adapting healthful eating and exercise behaviors to college life. Comments indicated that while college student activity levels differed from the past, there was consistent agreement that eating healthful diets was perceived to be a greater challenge in the transition to college. Male students were less concerned about weight and used fewer strategies to control weight gain than females. More work is needed to understand the transition of behaviors and in developing healthful lifestyles during college.