Gender, health, HIV risk, and demographic factors were examined with chi-square and logistic regression analyses to assess which of these factors are most predictive of active injection drug users' (IDUs') getting tested for HIV. Analyses were based on 36,898 IDUs recruited to participate in a nationwide multisite HIV prevention project. Women IDUs were recently tested (prior 6 months) more than men IDUs. Health factors, particularly for women IDUs, predicted who got tested for HIV more than risk or demographic factors. HIV testing usually occurred when disease symptomatology developed, after a long period of being capable of transmitting HIV to others, and when the benefits of AZT and other interventions may be reduced. Preventive interventions with IDUs are needed that emphasize the possible benefits of HIV testing and that encourage testing before symptoms develop.