Bracken fern (Pteridium aquilinum) is a worldwide plant containing toxic substances which represent an important chemical hazard for animals, including humans. Ptaquiloside (Pta), a norsesquiterpenoid glucoside, is the major carcinogen of bracken detected in the food chain, particularly in the milk from farm animals. To date ptaquiloside has been shown in the milk of cows feeding on a diet containing bracken fern. This is the first study which shows the systematic detection of Pta and reports its direct quantification in pooled raw milk of healthy sheep and goats grazing on bracken. Pta was detected by a sensitive method based on the chemical conversion of Pta into bromopterosine and following Gas Chromatography-Mass Spectrometry (GC-MS) analysis. The presence of ptaquiloside, possibly carcinogenic to humans, in the milk of healthy animals is an unknown potential health risk thus representing a harmful and potential global concern of food safety.