Background Law enforcement can shape HIV risk behaviours and undermine strategies aimed at curbing HIV infection. Little is known about factors that increase vulnerability to police victimization in Mexico. This study identifies correlates of police or army victimization (i.e., harassment or assault) in the past 6 months among patients seeking care at a free clinic in Tijuana, Mexico. Methods From January to May 2013, 601 patients attending a binational student-run free clinic completed an interviewer-administered questionnaire. Eligible participants were: (1) ≥18 years old; (2) seeking care at the clinic; and (3) spoke Spanish or English. Multivariate logistic regression analyses identified factors associated with police/army victimization in the past 6 months. Results More than one-third (38%) of participants reported victimization by police/army officials in the past 6 months in Tijuana. In multivariate logistic regression analyses, males (Adjusted Odds Ratio (AOR): 3.68; 95% CI: 2.19–6.19), tattooed persons (AOR: 1.56; 95% CI: 1.04–2.33) and those who injected drugs in the past 6 months (AOR: 2.11; 95% CI: 1.29–3.43) were significantly more likely to report past 6-month police/army victimization. Recent feelings of rejection (AOR: 3.80; 95% CI: 2.47–5.85) and being denied employment (AOR: 2.23; 95% CI: 1.50–3.32) were also independently associated with police/army victimization. Conclusion Structural interventions aimed at reducing stigma against vulnerable populations and increasing social incorporation may aid in reducing victimization events by police/army in Tijuana. Police education and training to reduce abusive policing practices may be warranted.