OBJECTIVE We examined the frequency and intensity of tobacco use and thoughts about abstinence among young adults in the United States as a function of their use of marijuana. We hypothesized that heavier marijuana use would be associated with heavier tobacco use and fewer attempts to quit smoking, and we explored relationships between marijuana use and ratings of intentions and thoughts related to quitting tobacco. METHODS This was a cross-sectional survey consisting of online recruitment and anonymous self-report. Participants were English literate, were between the ages of 18 and 25 years, and reported past-month tobacco use. More than half (53%) had smoked marijuana in the past 30 days. Tobacco use (quantity/frequency, Heavy Smoking Index, past-year quit attempt), thoughts about tobacco use (outcome expectancies, desire, self-efficacy, difficulty of quitting, abstinence goal, pros and cons, stage of change), alcohol use, and other drug use were assessed. RESULTS Compared with those who smoked only tobacco, cousers were younger and had smoked for fewer years; had higher household income; were more likely to be male, multiethnic, and nondaily smokers; and reported greater alcohol and other drug use. The variable of days using marijuana in the past 30 days was associated with multiple measures of tobacco use intensity/frequency. Only one association was significant between marijuana use and tobacco-related cognitions: Cousers had a lower likelihood of planning to quit tobacco for good (odds ratio = 0.75, 95% CI [0.58, 0.98]). CONCLUSIONS Findings support the association between tobacco and marijuana use among young people but speak to the importance of addressing tobacco cognitions in young adult smokers regardless of level of marijuana use.