This paper reports on the incidence of risk taking behaviours, and the relationship between risk perception and risk behaviours in a sample of 1245 Sydney injecting drug users (IDUs). Almost all respondents reported engaging in behaviours that placed them at risk of HIV infection: 32.9% through unsafe injecting, 84.4% because of unsafe sexual behaviour and 89.2% because of either injecting or sexual behaviour. Injecting and sexual behaviour were poorly correlated. This study also found that risk perception is unrelated to injecting or sexual behaviours, previous history of sexually transmitted diseases, a range of demographic characteristics including age and gender, and the number of times tested for HIV. Social policy and prevention programs should aim to change unsafe injecting and sexual behaviours directly, rather than attempting to achieve change indirectly by changing risk perception.