Nearly 10% of men and 20% of women in the U.S. have gallstones or will develop them at some time in life, yet most of those who have the condition do not realize it. In this case, what you don't know probably won't hurt you; gallstones that are simply floating around inside the gallbladder generally cause no symptoms and no harm.
These "silent" stones usually go unnoticed unless they show up in an ultrasound exam conducted for some other reason. However, the longer a stone exists in the gallbladder, the more likely it is to become problematic. People who have gallstones without symptoms have 20% chance of having an episode of pain during their lifetime.
When symptoms do occur, it's usually because the gallstone has moved and become lodged within a duct that carries bile, such as the cystic duct, a small conduit that connects the gallbladder to another tube called the common bile duct. The typical symptom is abdominal pain, perhaps accompanied by nausea, indigestion, or fever. The pain, caused by the gallbladder's contraction against the lodged stone, generally occurs within an hour of eating a large meal or in the middle of the night. Stones can also clog the common bile duct, which carries bile into the small intestine, and the hepatic ducts, which take bile out of the liver.
Obstructions in the bile pathway can cause a duct to become inflamed and possibly infected. Blockage of the common bile duct, which merges with the pancreatic duct at the small intestine, can also lead to inflammation of the pancreas (gallstone pancreatitis).
In a rare but dangerous condition that occurs most often in older women, gallstones migrate into the small intestine and block the passageway into the large intestine; symptoms include severe and frequent vomiting. Although gallstones are present in about 80% of people with gallbladder cancer, it is uncertain whether gallstones play a role, except when really large stones (greater than 3 centimeters in diameter) are present.