A 2-month-old girl presented with diarrhoea and skin rash. Initially suspected of having a viral infection, she was hospitalized because of persistent symptoms, dehydration and weight loss. Despite intravenous antibiotics, she only improved after switching to a hydrolysed formula. Later, she had severe reactions after reintroducing regular formula, raising suspicion of Food Protein-Induced Enterocolitis Syndrome (FPIES). Subsequently, the diagnosis was confirmed and soy formula and solid food were introduced.