This paper deals with a numerical and experimental study of ultrasound induced cavitation. On the basis of a computational analysis of Gilmore’s equation for the individual bubble dynamics, a slight decrease in the pressure radiated by a single bubble immediately before reaching the transient cavitation regime is predicted. Experiments presented in this paper confirm this observation. Therefore, a new method to detect the inception of transient cavitation is proposed. The numerical analysis of a single bubble behavior, carried out for the different bubble sizes, suggests that two distinct “types” of transient cavitation may occur in a cavitation field in connection with the relative number of bubbles involved in the process. The experiments seem to confirm the theoretical hypothesis. The experimental work consisted mainly of insonifying distilled water, with a gas content of about 75% of saturation, at 20 kHz and analyzing the resulting acoustic emissions.