Assessing the relative involvement of ethnic communities with illicit drugs relies on identification of ethnicity in collected information. Many of the indicators of ethnicity used in Victorian drug- and alcohol-related databases fail to provide researchers with adequate information to accurately determine ethnic or cultural orientation. Country of birth is the variable most commonly used to identify ethnicity, but it conceals Australian-born children of migrants who may identify primarily with their ethnic background. The self-identified 'ethnic/cultural background' variable collected in the Victorian methadone registry allowed us to show that many second-generation migrants do identify primarily with their ethnic/cultural background. Of the methadone permit forms examined, 31% identified the applicant as belonging to one of 70 different ethnic/cultural background groups. The most common ethnic groups were Vietnamese (22%), Greek (16%) and Italian (15%). The Victorian methadone registry implies that illicit drug use among a number of ethnic minority communities is substantial, unlike all other Victorian databases, which lack good ethnicity measures. Health-related databases should reflect the multi-cultural nature of the Victorian population; the inclusion of better ethnicity variables can allow an improved measurement about the extent of illicit drug use in ethnic minority communities and therefore illuminate a number of important education and service delivery issues.