Aim: Shoulder pain is the third most prevalent musculoskeletal condition that impairs function. Subacromial impingement syndrome is among the most typical causes of shoulder pain. The aim of this study was to evaluate inter-machine reliability of acromiohumeral distance measurements performed with standard ultrasound and wireless ultrasound devices in patients with subacromial impingement syndrome. Material and methods: A total of 61 participants diagnosed with subacromial impingement syndrome were included. Acromiohumeral distance was measured with wireless and standard ultrasound devices in a neutral position and at 60-degree abduction, respectively. The inter-machine intraclass correlation coefficient, standard error of measurements, and minimum detectable changes were calculated. Results: Inter-machine reliability measured in the neutral position was excellent (ICC = 0.97, 95% CI = 0.95–0.98); the standard error of measurement was 0.23 mm, and the minimum detectable change was 0.63 mm. Inter-machine reliability measured at 60 degrees abduction was excellent as well (ICC = 0.96; 95% CI; 0.93–0.97). The standard error of measurements was 0.20 mm, and the minimum detectable change was 0.55 mm. The mean difference between the two machines was 0.04 mm for the neutral position and 0.02 mm for the 60-degree abduction position. Conclusions: The study showed that wireless ultrasound devices were similar to standard ultrasound devices in measuring the acromiohumeral distance in patients with subacromial impingement syndrome. The findings could contribute to a significant improvement in the clinical use of wireless ultrasound devices.