Dysentery (UK pronunciation: , US: ), historically known as the bloody flux, is a type of gastroenteritis that results in bloody diarrhea. Other symptoms may include fever, abdominal pain, and a feeling of incomplete defecation. Complications may include dehydration.

The cause of dysentery is usually the bacteria from genus Shigella, in which case it is known as shigellosis, or the amoeba Entamoeba histolytica; then it is called amoebiasis. Other causes may include certain chemicals, other bacteria, other protozoa, or parasitic worms. It may spread between people. Risk factors include contamination of food and water with feces due to poor sanitation. The underlying mechanism involves inflammation of the intestine, especially of the colon.

Efforts to prevent dysentery include hand washing and food safety measures while traveling in countries of high risk. While the condition generally resolves on its own within a week, drinking sufficient fluids such as oral rehydration solution is important. Antibiotics such as azithromycin may be used to treat cases associated with travelling in the developing world. While medications used to decrease diarrhea such as loperamide are not recommended on their own, they may be used together with antibiotics.

Shigella results in about 165 million cases of diarrhea and 1.1 million deaths a year with nearly all cases in the developing world. In areas with poor sanitation nearly half of cases of diarrhea are due to Entamoeba histolytica. Entamoeba histolytica affects millions of people and results in greater than 55,000 deaths a year. It commonly occurs in less developed areas of Central and South America, Africa, and Asia. Dysentery has been described at least since the time of Hippocrates.