Flucytosine, or 5-fluorocytosine, a fluorinated pyrimidine analogue, is a synthetic antimycotic drug.
It is structurally related to the cytostatic fluorouracil and to floxuridine. It is available in oral and in some countries also in injectable form. A common brand name is Ancobon. Flucytosine was first synthesized in 1957 but its antifungal properties were discovered in 1964. The drug is dispensed in capsules of 250mg and 500mg strength. The injectable form is diluted in 250mL saline solution to contain 2.5g total (10mg/mL). The solution is physically incompatible with other drugs including amphotericin B.

It is on the World Health Organization's List of Essential Medicines, the most important medication needed in a basic health system.