Therapeutic ultrasound is one of the most used electrophysical agents in physiotherapy. Despite this important and widespread application, therapeutic ultrasound devices (TUSD) may operate outside the range recommended by the International Standard IEC 61689:2013, and, thus, may not contribute to the treatment (if the ultrasonic output power, UOP, used in clinical practice are lower than the nominal power, NP) or even aggravate the pre-existing injury (if the UOP used is higher than the NP). The aim of this study was to verify whether the UOP values emitted by three TUSD from the Physiotherapy Section of the Esquadrão de Saúde de Pirassununga (named as TUSD1, TUSD2 and TUSD3) were in accordance with the IEC 61689:2013. Additionally, statistical tests were employed to assess the repeatability of UOP measurements made with the TUSD on three different days. An acoustic radiation force balance was used to measure the UOP values emitted by TUSD in three days of testing by each equipment, which were configured to operate in continuous mode. In addition, 10 UOP measurements were performed for each NP value with all available frequencies and effective radiation area. TUSD, even with up-to-date maintenance, presented several values of UOP with relative error greater than that preconized by IEC 61689:2013 (81.39% of 1800 UOP measurements with TUSD1, 68.61% of 1800 UOP measurements with TUSD2 and 75.33% of 1200 UOP measurements with TUSD3). So, It is important that the professional responsible for monitoring the maintenance/calibration of this equipment is trained to interpret the reports prepared by companies that provide maintenance/calibration services.