Early cannabis use is associated with mental health and substance use (MHSU) challenges into adulthood. Given the vulnerability of youth who use cannabis, it is important to understand their clinical profiles and markers of risk. This cross-sectional descriptive study examines youth who began using cannabis during early adolescence compared to those who initiated at an older age. 634 youth and emerging adults (age M = 19.5, SD = 2.3; 46.5% female) were assessed at intake in a Canadian youth mental health and concurrent disorder out-patient service. Measures of demographic characteristics and MHSU were compared for youth who initiated cannabis use under the age of 14 versus 14 years or over. Nearly 30% of youth initiated cannabis use before age 14. Those who initiated cannabis early were younger and had distinct psychosocial risk factors. They were more likely to use cannabis (p = .005), tobacco (p = .006), powder cocaine (p = .030), and/or benzodiazepines (p = .033) at a high frequency. If they used other substances, they were more likely to have begun using them younger (all p < .001). Early initiators had more externalizing mental health symptoms (p = .024), crime/violence concerns (p < .001), and past trauma (p = .001). Distinct, clinically meaningful differences emerged between youth who initiated cannabis use early versus later. Early cannabis use is associated with multiple, overlapping needs. Cannabis use and concurrent MHSU should be systematically assessed from an early age, and prevention/promotion efforts should take early onset into account. Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.