Aim. The aim of this study was to investigate the validity of the Substance Misuse in Adolescence Questionnaire, which has been proposed as a screening instrument for problem drug use in adolescents. Participants and setting. The participants in the study were 4544 11-16-year-olds attending eight secondary schools located in the north-west midlands of England. Procedure. Participants completed an anonymous self-report questionnaire that incorporated a modified version of the SMAQ (the Assessment of Substance Misuse in Adolescence: ASMA), together with other questions relating to substance use and associated issues. Results. The ASMA showed good reliability, both within the overall sample of respondents, and in a drug-using subsample. Principal-components analysis returned a single factor when applied either to the whole sample or to the drug-using subsample; 1.4% of respondents met a criterion equivalent to that proposed by Swadi (1997) for 'problem drug use' (ASMA > 12). A further 6.4% reached a threshold for potentially problematic drug use (ASMA > 8) and could be considered 'at risk'. In regression analyses, ASMA scores were predicted by drug-related variables, and by low resistance to peer influence (RPI), but not by alcohol-related variables. The highest ASMA scores and lowest levels of RPI were found in heroin users. Respondents' perceptions of their future risk of drug or alcohol problems were predicted by RPI and by frequency of drug use and drunkenness. Conclusions. The ASMA may be a useful screening instrument for identifying problem drug use in adolescents unknown to treatment services.