BACKGROUND: Crystal methamphetamine (MA) is a powerful, highly addictive central nervous stimulant that can cause serious health consequences including neurotoxicity, paranoia, psychosis, depression, violence, and death. The objective of this study is to assess the prevalence and characteristics of MA use among two marginalized populations of youth (less than 30 years of age) in British Columbia. METHODS: A self-administered questionnaire was administered to a convenience sample of Vancouver street-involved youth (SY) and Lesbian/Gay/Bisexual/Transgender/Questioning (LGBTQ) centre youth in Vancouver and Victoria. Items measured include: participants' demographic characteristics; illicit substance use, including details of MA use; attempts at recovery and treatment; and potential consequences of MA use. RESULTS: One hundred and eighty of the 200 questionnaires distributed were completed. Sixty-seven percent of the SY and 24% of the LGBTQ youth reported ever having used MA. Of these: 43% had used within the last week; 46-57% used multiple times per day in their lifetime; they spent a maximum of 7-9 consecutive days awake; they began use in their middle to late teens; and half had sought help for a substance use disorder. SY who used MA within the last week were more likely to also use marijuana, cigarettes, heroin, ecstasy, and ketamine. Previous use of MA was associated with reports of auditory hallucinations. CONCLUSION: The current study demonstrates a high prevalence of MA use in two marginalized populations of youth. Use in sexual minorities, resulting psychopathology, and concurrent substance use all have important implications in delivery of service, prevention, and subsequent research.; (abstract from the article)