Chagas disease, also known as American trypanosomiasis, is a tropical parasitic disease caused by Trypanosoma cruzi. It is spread mostly by insects in the subfamily Triatominae, known as "kissing bugs". The symptoms change over the course of the infection. In the early stage, symptoms are typically either not present or mild, and may include fever, swollen lymph nodes, headaches, or swelling at the site of the bite. After four to eight weeks, untreated individuals enter the chronic phase of disease, which in most cases does not result in further symptoms. Up to 45% of people with chronic infections develop heart disease 10–30 years after the initial illness, which can lead to heart failure. Digestive complications, including an enlarged esophagus or an enlarged colon, may also occur in up to 21% of people, and up to 10% of people may experience nerve damage.

T. cruzi is commonly spread to humans and other mammals by the bite of a kissing bug. The disease may also be spread through blood transfusion, organ transplantation, consuming food or drink contaminated with the parasites, and vertical transmission (from a mother to her baby). Diagnosis of early disease is by finding the parasite in the blood using a microscope or detecting its DNA by polymerase chain reaction. Chronic disease is diagnosed by finding antibodies for T. cruzi in the blood.

Prevention focuses on eliminating kissing bugs and avoiding their bites. This may involve the use of insecticides or bed-nets. Other preventive efforts include screening blood used for transfusions. Early infections are treatable with the medications benznidazole or nifurtimox, which usually cure the disease if given shortly after the person is infected, but become less effective the longer a person has had Chagas disease. When used in chronic disease, medication may delay or prevent the development of end-stage symptoms. Benznidazole and nifurtimox often cause side effects, including skin disorders, digestive system irritation, and neurological symptoms, which can result in treatment being discontinued. New drugs for Chagas disease are under development, and experimental vaccines have been studied in animal models, a human vaccine has not been developed.

It is estimated that 6.5 million people, mostly in Mexico, Central America and South America, have Chagas disease as of 2019, resulting in approximately 9,490 annual deaths. Most people with the disease are poor, and most do not realize they are infected. Large-scale population migrations have carried Chagas disease to new regions, which include the United States and many European countries. The disease affects more than 150 types of animals.

The disease was first described in 1909 by Brazilian physician Carlos Chagas, after whom it is named. Chagas disease is classified as a neglected tropical disease.