BACKGROUND: Depression is common after stroke and is associated with increased mortality. However, there are few data on the prevalence after TIA, and it is unclear whether TIA can trigger depression and, if so, what factors might suggest susceptibility in an individual. METHODS: We completed a systematic review (Medline/PsychInfo/EMBASE searched to 20 March 2025) of published cross-sectional or cohort studies that reported the prevalence of depression at any time point after a TIA and validated the findings in an population-based cohort (Oxford Vascular Study; OXVASC). Pooled prevalence rates were calculated, risk factors reported and regression analyses were used to determine the proportion of between-study heterogeneity that could be accounted for by study methodology. RESULTS: The search identified 26 studies; 23 reported data at a uniform time point after the TIA but the prevalence rates of depression were highly heterogeneous at each time point studied (phet<0.001 at <1, 1-6 and 12 months). However, among studies with serial assessments (196 patients from 4 published longitudinal studies and 478 from OXVASC) there was less heterogeneity and the pooled prevalence of depression fell from 20.1% (16.9-23.4%;phet=0.35) at 0-1 month to 14.1% (11.5-16.7%;phet=0.40) at 3-12 months (pdiff=0.004). In the few studies that reported risk factors for depression after a TIA, younger age was the only consistent predictor, but this was similarly validated in the OXVASC population. On regression analysis for heterogeneity, 83% of the variance in prevalence rates between studies was explained by assessment method (postal questionnaire: 5.6%, 95%CI 3.1-8.1 versus face-to-face interview 17.7%, 13.7-21.7; p<0.001), the screening tool used, TIA definition and exclusion criteria. A model, based on these study methods in published studies, predicted a prevalence rate of 22.1% in OXVASC, which was close to the observed rate of 20.7% at 1-month validating the findings. CONCLUSIONS: Depression affects about 1-in-5 patients early after a TIA but prevalence falls with time, suggesting that it may be triggered by the event in some cases, but further work is required to identify risk factors. Additionally, when planning future research, investigators must remain cognisant of the significant influence that study design has on the observed prevalence rates.