Background and Objectives Concurrent use of cannabis and tobacco is associated with poor tobacco cessation outcomes. As little research has examined why treatment-seeking tobacco users engage in cannabis use, the objective of this study was to discover if emotional vulnerability and cannabis use motives are associated with concurrent users' cannabis use. Methods One hundred thirty-eight (n = 138) daily cigarette smokers seeking smoking cessation treatment completed measures of anxiety sensitivity, cannabis use motives, and cannabis use. Results Stronger coping, enhancement, social, and expansion motives were associated with using greater amounts of cannabis per use occasion. In a model accounting for all these motives, anxiety sensitivity moderated the relationship between enhancement motives and cannabis use. Discussion and Conclusions Clinical interventions for concurrent tobacco-cannabis users may be advanced by targeting low anxiety sensitive individuals' use of cannabis to increase excitement and fun. Such an approach may consist of having clients identify and engage in healthier pleasurable activities and by teaching clients to accept the trade-off between perceived less pleasurable, but healthier activities and cannabis use.