We have become increasingly aware of the presence of a type of image artifact normally appearing in anechoic areas (eg, cyst, bladder, gallbladder) and giving the appearance of "sludge" or "debris." These artifactual echoes may be caused by the fact that the finite width of the transducer beam pattern produces a finite thickness of the patient scan plane. All echoes produced in this "thick" scan plane are misinterpreted as being due to structures in the normally assumed "thin" scan plane. We have tested and verified this hypothesis by simulating soft tissue interfaces with 400 grit silicon carbide sandpaper in a water tank. A set of clues are proposed to enable the rapid identification of these artifacts.