Young injecting drug users (IDUs) in Australia are a group about whom little is known. It is suggested, however, that their drug using behaviours and life styles put them at particular risk for HIV/AIDS. Data collected in Perth from 195 respondents in the Australian National AIDS and Injecting Drug Use Study was analyzed with emphasis on the distinctions between young and older injecting drug users. It was found that, relative to those aged 23 or over, IDUs under 23 used more stimulants and LSD and fewer opiates and benzodiazepines; were more likely to inject all or most of their drugs; were less likely to have been in treatment; had more sex partners; were less likely to have changed their drug taking behaviour because of AIDS; were less likely to use alone; shared needles less frequently but shared at least some of the time; and had less knowledge of AIDS and were more pessimistic about the long term outcomes of AIDS. Such characteristics need to be taken into account if effective intervention and prevention strategies for this group are planned. Copyright © 1991 Carfax International Publishers.