Trends in the injection of methadone and benzodiazepines by injecting drug users (IDU) recruited in Sydney for the Illicit Drug Reporting System over the period 1996-2000 were examined. A total of 788 IDU were interviewed over the 5-year period. The proportion of IDU reporting recent methadone injecting declined significantly over the study period, from a peak of 31% in 1997 to 13% in 2000. Unlike the injection of methadone, there was no significant difference between the proportions of IDU reporting recent benzodiazepine injecting over the study period, which ranged between 10% and 16%. A consistent minority (range 5-7%) of IDU reported having injected both methadone and benzodiazepines in all years of the study. There were no differences in the proportions of males and females reporting recent methadone or benzodiazepine injecting in any individual year. Both methadone and benzodiazepine injecting were independently associated with higher levels of injection-related health problems. Given the substantial harms associated with these practices, continued monitoring of their prevalence is warranted.