Abstract: A combined ultrasonic imaging and dilatation catheter includes an inflatable dilatation balloon located at the distal end of a flexible catheter body. An ultrasonic imaging system including a fixed ultrasonic transducer and a rotatable reflective surface capable of deflecting an ultrasonic signal from the transducer is located adjacent to, but axially spaced-apart from the dilatation balloon. The dilatation balloon in the interior of the imaging housing are isolated, and separate lumens are provided for inflating the balloon and flushing the imaging housing. In this way, the balloon may be inflated with a contrast medium suitable for fluoroscopic imaging, while the imaging housing may be filled with a different medium suitable for ultrasonic imaging.