INTRODUCTION: Stigma is a major driver of harms associated with substance use and can interfere with the provision of high-quality, effective healthcare for people who use drugs. Our study aimed to explore the relationship between mental health clinicians' comfort in providing substance use care and their attitudes towards substance use. METHODS: In this cross-sectional study, the Brief Substance Abuse Attitudes Survey was administered among a convenience sample of mental health clinicians [N = 71] working in an acute care setting in Vancouver, Canada. One-way ANOVA and the Kruskal-Wallis test were used to examine the association between three levels of comfort and five predefined attitude subgroups. STROBE checklist for cross-sectional studies was used. RESULTS: Level of comfort was significantly associated with attitudes towards substance use across three subscales: permissiveness, nonstereotyping and treatment optimism. In pairwise comparisons, the neutral group held significantly less permissive attitudes when compared to the comfortable group. However, the neutral group held more stereotypical views and less optimism about treatment outcomes, when compared to the comfortable and uncomfortable groups, respectively. DISCUSSION AND CONCLUSIONS: Our findings highlight that mental health clinicians who are undecided or neutral about their comfort in providing substance use care are more likely to have negative views towards people with substance use disorders. Future work should explore, implement and evaluate education and training to reduce substance use disorder-related stigma among mental health clinicians and other health professionals.