Objective: To retrospectively correlate imaging findings post-sclerotherapy of low-flow vascular malformations with clinical outcome. Materials and Methods: We retrospectively evaluated 81 pediatric patients who had sclerotherapy in our department over a 14-year period. Patients with a diagnosis of low-flow vascular malformation, pre and post-treatment ultrasound (US) and clinical follow-up evaluation were included in the study. Exclusion criteria were coexisting high-flow vascular malformations, history of additional surgical or medical treatment to their malformation and large infiltrative lesions difficult to measure on US. Pre and post-treatment sonographic volumes of the malformation were assessed. Changes in volume were categorized into 6- increased volume, stable and volume decrease of 1-25%/26-50%/51-75%/75-100%. Clinical outcomes were categorized into 4 – worse, no change, improved and symptom free. In cases where pre-treatment MRI was available, the estimated malformation volumes in both modalities were correlated using Spearman’s rank correlation. The change in sonographic volume was correlated with clinical outcome using Spearman’s rank correlation. P-values < .05 were considered significant. Results: Twenty-nine patients were included in the study; 13 with venous malformation (VM), and 16 with lymphatic malformation (LM). Nineteen patients had both pre-treatment US and MRI, showing correlation in volume between the 2 modalities ( P < .001). Post-treatment change in volume correlated with clinical outcome for combined venous and LMs (rho = .44, P = .02). No correlation was found when venous (rho = .48, P = .09) and lymphatic (rho = .33, P = .21) malformations were considered separately. Conclusion: Ultrasound can potentially be used as an objective tool in evaluating sclerotherapy treatment response of low-flow vascular malformations in the pediatric population.