OBJECTIVE: Trauma exposure is common in preschool-aged children. Understanding the psychological impact of such exposure and the prevalence of posttraumatic stress disorder (PTSD) in this population is important for provision of appropriate and timely intervention. This pre-registered (PROSPERO: CRD41019133984) systematic review and meta-analysis examined the prevalence of PTSD in trauma-exposed preschool-aged children. METHOD: Literature searches were conducted of PubMed (Medline), PsycINFO and PILOTS, alongside reference lists of relevant reviews. Studies were selected if they comprised trauma-exposed samples with a mean age of less than 6.5 years, and PTSD was assessed using standardized interviews at least 1-month post trauma. Information on sample characteristics, trauma exposure, PTSD measurement, and diagnostic criteria were extracted. For studies that applied more than one PTSD diagnostic algorithm, the most age-appropriate criteria were used to estimate pooled prevalence estimate across studies. A random-effects model was used for meta-analysis. RESULTS: Eighteen studies were included (N = 1941). The pooled PTSD prevalence was 21.5% (95% CI = 13.8%-30.4%) when using the most developmentally appropriate diagnostic algorithm that was available. When focusing on the subset of studies that reported both standard adult criteria and age-appropriate criteria (k = 12), a pooled estimate of 4.9% (95% CI = 2.5%-8.0%) was obtained for standard adult criteria (DSM-IV), and 19.9% (95% CI = 12.1%-29.0%) was obtained for age-appropriate criteria (PTSD-AA). Prevalence was 3-fold higher following interpersonal and repeated trauma exposure, compared to non-interpersonal or single-event trauma, respectively. Higher prevalence was found when age-appropriate diagnostic tools were used. There was significant heterogeneity across studies and a lack of studies conducted in low-income countries and applying age-appropriate diagnostic algorithms. CONCLUSION: Preschool-aged children are vulnerable to developing PTSD following trauma exposure. Younger children show prevalence trends similar to those of older youths and adults following different types of trauma. Age-appropriate diagnostic criteria are essential to ensure that appropriate identification and early support are provided.