Measures assessing marijuana-related consequences or problems experienced by young adults have typically been adapted from measures assessing alcohol consequences. These measures may not fully reflect the specific unwanted or perceived "not so good" effects of marijuana that are experienced by young adults. Thus, using these measures may present a gap, which needs to be addressed, given that reports of consequences are often utilized in brief motivational personalized feedback interventions. Data from three different studies of young adults were used to (1) examine self-reported "not so good" effects or consequences of marijuana use among frequent marijuana-using college students (Study 1), (2) create a new version of a marijuana consequences list and compare it to an existing marijuana consequences measure (Study 2), and (3) assess convergent and divergent validity between a finalized Marijuana Consequences Checklist (MCC, 26-items) and marijuana use and risk for cannabis use disorder (Study 3). The most frequently endorsed self-reported effects of marijuana included the impact on eating (the "munchies"), dry mouth, trouble concentrating, and acting foolish or goofy. Higher scores on the MCC were associated with more frequent use and a higher probability of meeting criteria for cannabis use disorder. The MCC represents a range of negative consequences of marijuana use derived from frequent users' own accounts and includes consequences not assessed by other measures. The MCC captures marijuana-specific negative consequences relevant for young adults, which can be incorporated in brief motivational personalized feedback interventions.