Background: Childhood maltreatment has been associated with a range of adverse mental and psychosocial outcomes, but its association with subsequent injecting drug use (IDU) is less clear. This study investigates the associations between specific and multiple forms of substantiated childhood maltreatment and IDU reported at 21 years. Method: The Mater-University of Queensland Study of Pregnancy is a prospective birth cohort study. It recruited pregnant women at their first antenatal clinic visit and collected data on their children at 21 years. Data from 3750 participants (1769 males and 1981 females) were analysed using agency substantiated childhood maltreatment from birth to 14 years of age and self-reports of ever IDU at 21 years. We used multivariable logistic regression analyses to control for possible confounders. Results: The sample's mean age was 20.6 years. Some 4.1% (n = 72) of males and 4.6% (n = 91) of females had experienced substantiated childhood maltreatment. The prevalence of IDU was 6.6% (n = 118) and 4.6% (n = 91) for males and females, respectively. In adjusted models, all forms of substantiated childhood maltreatment, with the exception of sexual abuse, were associated with IDU in females (adjusted odds ratios (AORs) = 2.69–3.02) but only emotional abuse (AOR = 2.51) was associated with IDU in males. Multiply occurring forms of childhood maltreatment were also associated with IDU in females (AORs = 2.36–3.41) but not in males. Conclusions: Injecting drug use appears to be an adverse outcome of childhood maltreatment particularly in females. Additional research is needed to better understand why females appear to be more affected than males.