Objective: To compare the accuracy of ultrasound (US)-guided versus unguided pes anserinus bursa injections in a cadaveric model. Design: Single blind, prospective study. Setting: Academic institution procedural skills laboratory. Participants: Twenty-four unembalmed, unpaired adult cadaveric lower extremity specimens. Methods: A single investigator performed 12 US-guided and 12 unguided pes anserinus bursa injections using colored liquid latex into 24 unembalmed adult cadaveric lower extremity specimens. The order of the injection techniques was randomized. The specimens were subsequently dissected by a co-investigator blinded to the injection technique used for each injection. Main Outcome Measures: The injections were graded for accuracy as follows: accurate (all injectate contained within the pes anserinus bursa), accurate with overflow (injectate within the pes anserinus bursa, but also located in adjacent structures), or inaccurate (injectate not within the pes anserinus bursa). The accuracy of the 2 approaches was compared using Pearson x2 test with Williams' correction for the small sample size (P = .05). Results: The accuracy rate was 92% (11 of 12 specimens) in the US-guided condition and 17% (2 of 12 specimens) in the unguided condition. One US-guided injection was considered accurate with overflow, whereas 4 unguided injections were accurate with overflow. The US-guided injection technique was significantly more accurate than the unguided technique (Williams-corrected x2 = 12.528, P < .01). Conclusions: Despite its superficial location, unguided pes anserinus bursa injections rarely place the injectate within the pes anserinus bursa, whereas US-guided pes anserinus bursa injections have a high degree of accuracy. Therefore, clinicians should consider using US-guidance for diagnostic or therapeutic pes anserinus bursa injections when indicated.