Montezuma's revenge is a colloquialism for the diarrhea contracted in Mexico and other Latin American countries by non-locals. The term dates from the conquering of local people by European countries. The diarrhea and discomfort is thought to be the revenge of the local gods that were worshipped prior to Latin American countries becoming Christianized.

Montezuma's revenge is, however, not an infliction by an angry god, but the body’s response to bacterial or parasitic agents encountered in water sources and in produce. Montezuma's revenge can occur not only in Latin American countries but also in other developing countries where water may not be treated to eliminate amoebas or bacteria responsible for illness. Improper washing of vegetables and fruit can also result in a case of Montezuma's revenge.

In many cases, Montezuma's revenge is a transient illness. The best treatment tends to be taking Pepto Bismol®, or bismuth sulfate. However, children experiencing diarrhea and fever should not be given bismuth sulfate as it contains salicylic acids, which are indicated in developing Reye’s syndrome.

If bismuth sulfate does not resolve the condition, and if a fever develops, this may be indication of parasitic or bacterial infection that is not easily destroyed by the body’s natural immunities. In these cases, those with Montezuma's revenge may also require antibiotics or anti-parasitic medications to cure the condition.

Montezuma's revenge can frequently be avoided by not consuming the water or produce of a region where it occurs. Drinking bottled water, even when brushing the teeth, is recommended to reduce exposure. Mexico, in particular, is known for attractive blended drinks like the margarita. Ice may also be made from unbottled water and result in Montezuma's revenge, so such drinks should be avoided.

Since Mexico and parts of Latin America can be extremely warm, it is important to keep fluid intake high, especially if one has a case of Montezuma's revenge. Medical experts recommend avoiding beverages containing either alcohol or caffeine. Bottled local sodas that do not contain caffeine are considered safe for consumption, and can make consuming at least six to eight glasses of fluids a day a little less of a chore. However, high sugar products may fuel diarrhea, so if diarrhea worsens upon consuming sodas, switching to water is recommended.

Montezuma's revenge that continues when one has returned home is almost always due to bacterial or parasitic infection. If Montezuma's revenge continues in this manner, or is accompanied by high fever, and/or vomiting, this may necessitate hospitalization, intravenous antibiotics, and intravenous fluids to prevent severe dehydration.