Ultrasound examination of small cysts in vivo and in vitro has demonstrated that several factors can interfere with recognition of their true anechoic nature. Reverberation and the effects of the beam width can interact with adjacent acoustic reflectors to produce artifactual echoes. Sonic enhancement in distal tissues varies with time gain compensation, frequency, and the position of the focal zone. If the operator is aware of this problem, he can compensate for these effects and thereby improve diagnostic accuracy.