Assisted injection among injection drug users (IDUs) remains understudied. We recruited 1056 injecting drug users (IDUs) using respondent driven sampling in Tijuana, Mexico. Participants underwent HIV and syphilis testing and structured interviews. One quarter (25%) sought injection assistance in the past 6 months. Seeking injection assistance was independently associated with being female [Adjusted Odds Ratio (AOR)=2.59; 95% Confidence Interval (CI)=1.73–3.90], being born outside Baja California (AOR=1.75; CI=1.26–2.42), having recent abscesses (AOR=2.59; CI=1.93–3.47), using syringes previously used by others in the past six months (AOR=1.99; CI=1.45–2.71), and ever being arrested for carrying sterile syringes (AOR=1.55; CI=1.15–2.09).