We have evaluated the possible phototoxicity of an orange‐based diet on sheep in a controlled environment. The phototoxic effect of psoralens, potent phototoxic furocoumarins, contained in oranges could be manifested either as a perioral contact phototoxicity or as a postingestion phototoxic effect. This research has especial relevance in the region of Valencia, Spain, where sheep are occasionally fed large quantities of these agricultural by‐products and where sunlight is constant year‐round. Ewes were randomly allocated to two groups, one to be fed a maintenance diet (n = 9), and the other to receive, after a brief adaptation period, solely oranges (n = 6). The ewes were placed in an external enclosure and fed this diet for 2 months. At approximately 3‐week intervals, the ewes were subjected to thorough clinical and dermatological examination. Skin biopsies were obtained on two different occasions. All procedures were carried out under the guidelines of the local ethics committee. The sheep on the orange diet showed weight loss and a debilitated condition. However, during the study, no clinical or pathological signs of oral or systemic photodermatitis were observed. Funding: Self‐funded.