Data from two large surveys -- the Sydney component of the ANAIDUS (Injecting Drug Use Study), conducted in 1989, and the ASHIDU (Australian Study of HIV and Injecting Drug Use), conducted in 1994 -- were used to examine the issue. Together, these studies contained information on 1,292 individuals who identified themselves as heroin users. Although there were no significant gender differences in age of initiation to heroin use, there was a significant (p < 0.001) time trend in the mean age at which heroin was first used. Specifically, the mean age of first heroin use among individuals born during the interval 1940-1949 was 20.5 years, and among those born during 1970-1979 the mean age of first heroin use was 16.5 years. These findings were confirmed by analyses of the National Household Survey. Further analysis of the ASHIDU data indicated that younger age of initiation to heroin use was associated with polydrug use, overdose, and crime after the effects of duration of heroin use had been statistically controlled. These findings suggest that there has been both an increase in the willingness of youth to experiment with heroin and an increased availability of the drug over this time. In combination with evidence that there has been an increase in the amount of heroin being imported into Australia, as well as an increased demand for treatment for opiate dependence, these data suggest that Australia is experiencing an increase in the use of heroin, particularly among youth. 3 tables and 26 references