Biliary sludge is usually seen on transabdominal sonography as low-level echoes that layer in the dependent portion of the gallbladder without acoustic shadowing. Synonyms for biliary sludge include microlithiasis, biliary sand or sediment, pseudolithiasis, and microcrystalline disease. In most patients, biliary sludge is composed of calcium bilirubinate and cholesterol monohydrate crystals. A variety of predisposing factors are associated with biliary sludge formation. In most of these patients, removal of the risk factor can lead to resolution of sludge. In asymptomatic patients, biliary sludge can be managed expectantly. In patients who develop biliary-type pain, cholecystitis, cholangitis, or pancreatitis, the treatment of choice is cholecystectomy for those who can tolerate surgery. In patients who are not operative candidates, endoscopic sphincterotomy can prevent further episodes of cholangitis and pancreatitis, whereas medical therapy with ursodeoxycholic acid can prevent sludge formation and recurrent acute pancreatitis.