Background and Purpose--Posttraumatic stress disorder (PTSD) can be triggered by life-threatening medical events such as strokes and transient ischemic attacks (TIAs). Little is known regarding how PTSD triggered by medical events affects patients' adherence to medications. Methods--We surveyed 535 participants, age ≥40 years old, who had at least 1 stroke or TIA in the previous 5 years. PTSD was assessed using the PTSD Checklist-Specific for stroke; a score ≥50 on this scale is highly specific for PTSD diagnosis. Medication adherence was measured using the 8-item Morisky scale. Logistic regression was used to test whether PTSD after stroke/TIA was associated with increased risk of medication nonadherence. Covariates for adjusted analyses included sociodemographics, Charlson comorbidity index, modified Rankin Scale score, years since last stroke/TIA, and depression. Results--Eighteen percent of participants had likely PTSD (PTSD Checklist-Specific for stroke ≥50), and 41% were nonadherent to medications according to the Morisky scale. A greater proportion of participants with likely PTSD were nonadherent to medications than other participants (67% versus 35%, P<0.001). In the adjusted model, participants with likely PTSD were nearly 3 times more likely (relative risk, 2.7; 95% CI, 1.7–4.2) to be nonadherent compared with participants without PTSD (PTSD Checklist-Specific for stroke <25) even after controlling for depression, and there was a graded association between PTSD severity and medication nonadherence. Conclusion--PTSD is common after stroke/TIA. Patients who have PTSD after stroke or TIA are at increased risk for medication nonadherence