The application of a novel continuous cooling crystallization system coupled with ultrasound technology to crystallize adipic acid from an aqueous solution was investigated. Both continuous ultrasound irradiation and silent (control) regimes were used in order to elucidate the effects of unstable cavitation on the duration of the transient period, steady state operating conditions, crystal habit, and particle size distribution. The results reveal that under continuous ultrasonic irradiation the steady state particle size distribution is achieved after shorter times, with a consistent reduction of the steady state supersaturation resulting in increased product yields relative to silent continuous crystallization experiments. Continuous crystallization with ultrasonic irradiation results in significantly smaller crystal sizes, reduced agglomeration and an improved habit of crystals. Furthermore, the influence of mean residence time using continuous ultrasound produces a smaller change in particle size and size distribution. Finally, the experiments reveal a noticeable reduction of the fouling on non-cooling surfaces and underline the need for intermittent discharge to prevent classification on withdrawal product. (C) 2010 Elsevier Ltd. All rights reserved.