Abstract: An apparatus and method for transilluminating a tubular tissue within the body. The apparatus comprises an elongate catheter having a fiber optic substantially coextensive with the length thereof which provides diffuse illumination laterally along at least a portion of the length of the catheter. The fiber optic terminus at the proximal end of the catheter is flared to form a light receiving aperture for collecting illuminating light. The flared proximal end of the optical fiber presents an effectively greater light input aperture and enables the fiber to conduct more light to the distal delivery end than would otherwise be possible with a fiber having a flat cut end and receiving light from a divergent light source. The distal end of the catheter is dimensioned to fit within a tubular tissue and be advanced therethrough.