Cow's milk protein (CMP) is usually one of the first complementary foods to be introduced into the infant's diet and is commonly consumed throughout childhood as part of a balanced diet. CMP is capable of inducing a multitude of adverse reactions in children, which may involve organs like the skin, gastrointestinal (GI) tract or respiratory system. The diagnosis of CMP-induced adverse reactions requires an understanding of their classification and immunological basis as well as the strengths and limitations of diagnostic modalities. In addition to the well-recognised, immediate-onset IgE-mediated allergies, there is increasing evidence to support the role of CMP-induced allergy in a spectrum of delayed-onset disorders ranging from GI symptoms to chronic eczema. The mainstay of treatment is avoidance of CMP; this requires dietetic input to ensure that this does not lead to any nutritional compromise. This review is intended to highlight the broad spectrum of manifestations of CMP allergy and to offer an approach to the diagnosis and treatment thereof.