Intro. Alcohol and marijuana are the most widely used substances among Argentinean university students, and their simultaneous (SAM) use is common. Compared to single-substance use, SAM use increases acute and long-term risks. This study extends previous research conducted in Córdoba (CBA) by incorporating a cohort from Mar del Plata (MDQ). We compared frequency of SAM use and associated problems and examined in the MDQ sample if SAM use motives and impulsivity explained negative consequences. Method. A cross-sectional analytical study was conducted in students aged 18–30 years from universities in CBA and MDQ, who completed an online questionnaire. Descriptive analyses and tests of proportion/mean differences between sites were performed. A hierarchical regression analyzed if SAM use motives explaining negative consequences in MDQ sample, beyond impulsivity traits. Results. MDQ Students showed higher frequency of SAM use than CBA peers, regardless sex and age of onset; yet problems were similar across sites. SAM use motives explained SAM-related consequences (R²=.253; ΔR²=.134; p<.01), after controlling for impulsivity. Negative urgency and social motives were significant predictors (p<.05). Conclusions. The results underscore that SAM use can vary across the country. Negative consequences of SAM were mainly predicted by negative urgency and social motives, highlighting the need for interventions focused on emotion regulation and peer dynamics.