In recent years, there has been an increase in the application of ultraviolet (UV) light as an alternative to chemical disinfection technologies. However, in the case of poor quality effluents, the practical limit of UV disinfection of wastewater is dictated by disinfection-resistant, particle-associated bacteria. Although these particles may be removed by filtration, an alternative method to reduce the impact of suspended particles on disinfection efficiency is to decrease particle size using ultrasound technology. Mechanical forces exerted on particles due to the collapse of cavitation bubbles created by sonication break suspended particles into small fragments. In this paper, a critical review of ultrasound application for wastewater treatment is presented with emphasis on disinfection. Much of the work in this area remains at the laboratory scale. As a result, there is a need for fundamental information regarding the effect of sonication on the kinetics of disinfection and interaction of ultrasound with suspended particles. Such information is necessary for process engineering, design, and scale-up of ultrasound systems.