Ultrasonic power transducers are commonly used in applications like cleaning, plastics welding or sonochemistry. Typically, the design of transducers for new applications is a tedious iterative process of design, prototype construction and tests. The transducers must fulfill the needs and restrictions of the specific application, as otherwise the transducer might be oversized or fail during operation. While reliability has been studied worldwide intensively in the case of piezoelectric multilayer actuators—driven by car industry which now uses such actuators in their fuel injection systems—nearly no literature is available for the reliability of ultrasonic power transducers. As well, manufacturers seldom present data about aging or lifetime of their components. To enhance the knowledge about typical failure mechanisms of ultrasonic power transducers under different load conditions, our contribution—as a first step—reports on a theoretical study on the reliability of common known ultrasonic transducers and gives some examples of typical failures and their influence on the characteristics of the transducer.