Emerging adulthood is a developmental period marked by increased risky behaviours, including alcohol and cannabis co-use (AC co-use). AC co-use is associated with more health and occupation-related negative consequences compared to the isolated use of any one of these substances. Several studies examine co-use as a dichotomy (i.e., whether someone co-uses or not), which limits our understanding of the heterogeneity of co-use profiles and its impact on negative consequences. Furthermore, given emerging evidence supporting gender differences in negative consequences experienced specific to AC co-use, it is critical to consider how gender may influence the nature of emerging adult co-use profiles, determinants, and consequences. The present study addresses these limitations by pursuing three core objectives: (i) identify single and co-use patterns across gender; (ii) examine personality factors (i.e., impulsivity) as a predictor of patterns; (iii) link patterns with negative consequences to measure risk. This online study included 468 first-year undergraduate participants who completed measures of alcohol and cannabis quantity and frequency of use, impulsivity, and negative consequences for both alcohol and cannabis use. Latent profile analyses revealed four AC co-use patterns. Two were identical across gender: Profile 1 – Heavy Alcohol Single Use and Elevated Alcohol Co-Use and Profile 2 – Primarily Moderate Alcohol Single Use. Profile 4 (Light AC Single Use and Elevated Alcohol Co-Use) was also highly similar across genders. However, gender-diverse individuals and women tended to use and co-use cannabis to a greater extent than men. In contrast, Profile 3 differed in women relative to men and gender-diverse individuals. Indeed, women in this profile primarily heavily use alcohol on co-use days (Primarily Heavy Alcohol Co-Users); men and gender-diverse individuals displayed a more problematic pattern (Heavy Cannabis Single Use and Elevated Alcohol Co-Use) involving heavy use and co-use of cannabis, coupled with a heavy co-use of alcohol. Interestingly, however, predictions and outcomes generalized across genders, suggesting that despite these differences in patterns, these profiles seem to capture similar psychological mechanisms. Consistent with our hypotheses, two facets of impulsivity (i.e., negative urgency and sensation-seeking) predicted risky AC co-use patterns. However, another facet (positive urgency) was related to less problematic AC co-use patterns. More negative consequences were associated with the heaviest co-use pattern (i.e., Profile 3). Unexpectedly, Profile 4 (also displaying high AC co-use) was associated with a similarly high level of negative consequences. Profile 1 (dominated by alcohol use and co-use) also had a similar level of alcohol-related negative consequences as Profiles 3 and 4. Our findings add meaningful implications and improve refined measurement of AC co-use. Furthermore, this study has contributed to risk model etiology which will further the literature and have clinical implications.