Introduction The young adult years have been recognized as an influential period for excess weight gain. Non-traditional students and those attending 2-year community colleges are at particularly high risk for a range of adverse weight-related outcomes. Design Choosing Healthy Options in College Environments and Settings was an RCT with students randomly assigned into a control or intervention condition after baseline assessment. The study was designed to evaluate if a 24-month weight-gain prevention intervention reduces the expected increase in BMI and overweight prevalence in young adults attending 2-year colleges. Two cohorts were recruited, corresponding to the fall and spring semesters. Data collection occurred at four time points for each cohort, with baseline occurring in fall 2011 for Cohort 1 and spring 2012 for Cohort 2. The 24-month follow-up occurred in fall 2013 for Cohort 1 and spring 2014 for Cohort 2. Data analysis occurred in 2015–2016. Setting/participants This research was conducted with 441 students from three community colleges in Minnesota. Intervention The 24-month intervention began with a 1-credit college course on healthy weight behaviors. A social networking and social support website was introduced as part of the course and participation encouraged for the duration of the trial. Main outcome measures Changes in BMI, weight, body fat percentage, waist circumference, and weight status were assessed. Results Retention of the cohorts at 24 months was 83.4%. There was not a statistically significant difference in BMI between conditions at the end of the trial. However, there was a statically significant difference in the prevalence of overweight/obesity between treatment conditions at 24 months. Also, participants randomized to the intervention who were overweight or obese at baseline were more than three times as likely to transition to a healthy weight by the end of the trial as compared with control students. Conclusions The intervention was not successful in achieving BMI differences between treatment groups. However, an 8% reduction in the prevalence of overweight and obesity over time may have population-level significance. Trial registration This study is registered at www.clinicaltrials.gov NCT01134783.