Background: Diagnostic ultrasound (US) is a commonly used imaging modality for visualising tendon pathology and morphology. In comparison to magnetic resonance imaging (MRI), diagnostic US is perceived to have a higher risk of error when evaluating tendon size.Aim: To systematically assess the evidence regarding the Intra rater and Inter rater reliability of diagnostic US measurements of tendon size.Data sources: Eight electronic databases were searched using an agreed set of keywords. Studies which investigated the reliability of tendon, size (thickness or cross sectional area) using diagnostic US were eligible.Results: Combined Inter rater and Intra rater ICC values for tendon thickness ranged from 0.45 to 0.99. Combined Inter rater and Intra rater ICC values for tendon cross-sectional area (CSA) ranged from 0.58 to 0.92. Overall, Intra rater ICC values (0.59-0.99) were marginally higher than Inter rater values (0.45 0.99) across all tendon sites. Percentage co-efficient of variation (CV%) for tendon thickness and CSA ranged from 0 to 35% across all tendons. Percentage standard error of the mean SEM% values for tendon thickness ranged from 3.33% to 7.39%.Conclusions: The findings of this review suggest diagnostic US measures of tendon size are reliable, both in terms of relative and absolute reliability. However, the findings must be considered in light of the presence of tendon abnormalities in a large percentage of asymptomatic populations. (C) 2016 Elsevier Ltd. All rights reserved.