AbstractAimsTo investigate the reliability, validity, and level of evidence of applying ultrasound in assessing the lower‐limb muscles of patients with cerebral palsy (CP).MethodPublications in Medline, PubMed, Web of Science, and Embase were searched on May 10, 2023, to identify and examine relevant studies investigating the reliability/validity of ultrasound in evaluating the architecture of CP lower‐limb muscles systematically, following the Preferred Reporting Items for Systematic Reviews and Meta‐Analysis 2020 guidelines.ResultsOut of 897 records, 9 publications with 111 CP participants aged 3.8–17.0 years were included (8 focused on intra‐rater and inter‐rater reliability, 2 focused on validity, and 4 were with high quality). The ultrasound‐based measurements of muscle thickness (intra‐rater only), muscle length, cross‐sectional area, muscle volume, fascicle length, and pennation angle showed high reliability, with the majority of intraclass correlation coefficient (ICC) values being larger than 0.9. Moderate‐to‐good correlations between ultrasound and magnetic resonance imaging measurements existed in muscle thickness and cross‐sectional area (0.62 ≤ ICC ≤ 0.82).InterpretationGenerally, ultrasound has high reliability and validity in evaluating the CP muscle architecture, but this is mainly supported by moderate and limited levels of evidence. More high‐quality future studies are needed.