For medical devices, a usability assessment is mandatory for market access; the objective is to detect potentially harmful use errors that stem from the device's design. The manufacturer assesses the final version of the device and determines the risk-benefit ratio for remaining errors. Nevertheless, the decision rule currently used to determine the sample size for this testing has statistical limitations and the lack of a clear decision-making perspective. As an alternative, we developed a value-of-information analysis from the medical device manufacturer's perspective. The consequences of use errors not detected during usability testing and the errors' probability of occurrence were embedded in a loss function. The value of further testing was assessed as a reduction in the expected loss for the manufacturer. The optimal sample size was determined using the expected net benefit of sampling (ENBS) (the difference between the value provided by new participants and the cost of their inclusion).