Reliability of quantifying intratendinous blood flow (IBF) assessed with the high-sensitive Doppler ultrasound Advanced dynamic flow (ADF) has not been examined, yet. Therefore, this study aimed to investigate intra- and inter-observer reliability of evaluating Achilles tendon IBF assessed with ADF using established scoring systems. Three investigators evaluated IBF in 67 recordings in a test-retest design applying the Ohberg score (OS), a modified Ohberg score (MOS), and a counting score (CS). Intra-and inter-observer agreement for OS and MOS was analysed with Cohen’s Kappa and Fleiss Kappa (absolute), Kendall’s tau b and Kendall’s Coefficient of Concordance (Kendall’s W) (relative). Reliability of CS was analysed with ICC 2.1 and 3.1, standard error of measurement (SEM) and Bland-Altman analysis (bias and limits of agreement (LoA)). Intra- and inter-observer agreement (absolute/relative) ranged from 0.61-0.87/0.87-0.95 and 0.11-0.66/0.76-0.89 for OS, and from 0.81-0.87/0.92-0.95 and 0.64-0.80/0.88-0.93 for MOS, respectively. CS revealed an intra-observer ICC of 0.94-0.97, SEM 1.0-1.5, and bias -1, LoA 3-4 vessels. Inter-observer ICC for CS ranged from 0.91-0.98, SEM 1.0-1.9, and bias 0, LoA 3-5 vessels. MOS and CS showed excellent reliability and seem convenient for research and clinical practice. OS revealed decent intra- but unexpected low inter-observer reliability and therefore cannot be recommended.