Adolescents' health is today threatened by the use of alcohol and other psychoactive substances. It is therefore important to develop interventions related to substance use in school health care. The aim of this study was to examine the empowering or risk background factors related to substance use among adolescents, and the ability of school nurses (PHN) to identify these factors and to provide needed individual early intervention. The data were collected by semistructured questionnaires completed by 14- to 18-year-old adolescents (n = 326, response rate 79) and PHNs (n = 10) in 2004. The adolescent questionnaire consisted of items related to the respondents' background and Adolescents' Substance Use Measurement (ADSUME). Following individual consent, adolescents' ADSUME responses were sent to the PHNs for intervention. The PHNs assessed the adolescents' empowering background factors and intervention using the questionnaire, and 70% (n = 228) of their answers matched the adolescents' answers. The data were analysed with the SPSS software using the chi-squared test, Fisher's exact test, kappa coefficient and agreement percentages. Substance use among adolescents was associated with parental support, mother's education and smoking, the adolescents' knowledge about substances, peer support and hobbies. The PHNs' assessments regarding supportive background were not in agreement with the assessments of adolescents who were using hazardous substances. One-fifth of the adolescents received the brief intervention, although many of them might have needed extra support and follow-up on the basis of their ADSUME results. The research findings can be generalized only for alcohol use, because only 3% of the study informants used substances other than alcohol. Further research is warranted concerning PHNs' ability to identify hazardous substance use and to ensure preventive early intervention and requisite support among substance-using adolescents in order to improve evidence-based health promotion.