Acute biliary tract disease complicated intrauterine pregnancy in 26 patients seen during a 5 year period. Biliary symptoms were distinct and occurred during the first trimester in 7 patients, the second trimester in 5 patients, the third trimester in 12 patients, and in two early postpartum patients. Nine patients had marked hyperamylasemia which resolved with medical management, and no severe cases of pancreatitis occurred. Ultrasonography was used to confirm the presence of gallstones in 18 patients and demonstrated dilated intrahepatic ducts in one of two patients with surgically proved choledocholithiasis. Nineteen patients had cholecystectomy and cholangiography, and 4 had common bile duct explorations. Only two of seven patients who presented in the first trimester had term pregnancy. Diagnosis of cholelithiasis in pregnancy by ultrasonography is accurate and reliable. The risk to the fetus of radionuclide scanning and conventional radiography is not justified. Secondary hyperamylasemia is common but responds to conservative therapy. Operation may be delayed until delivery in most patients, with urgent exploration reserved for uncertainty in diagnosis, choledocholithiasis, or acute cholecystitis that does not resolve with medical measures.