Background The incidence of venous thromboembolism in children has increased dramatically, with most cases occurring in children with cancer, surgery, trauma, congenital heart disease, and systemic lupus erythematosus. Early assessment of risk factors present in children would minimize morbidity and mortality from these events. Objectives To evaluate the reliability and validity of a tool for assessing risk for venous thromboembolism in children. Methods The tool was developed after a review of the literature with assessment of content validity by a multidisciplinary team of experts. Patients’ charts were reviewed retrospectively to establish reliability and validity of the tool. A P value less than .05 was considered statistically significant. Results Thirty-five charts were assessed for tool validity and were found to be statistically significant for all 3 risk score assessment categories. Logistic regression was used to assess 1001 patients’ charts for internal consistency, which was found to be high (χ 2 5 [n = 1001] = 100.6, P < .001). Results indicated that most patients at risk for venous thromboembolism were between the ages of 13 and 17 years, with females having more than 7 times greater risk than males. Conclusions Descriptive statistics show that the assessment tool displays strong reliability and validity. Results validated a significant relationship between the risk score and the incidence of venous thromboembolism. Findings suggest that use of the assessment tool could significantly reduce adverse outcomes associated with venous thromboembolism in children.