The term malnutrition refers to both undernutrition and overnutrition. In healthcare, it most often refers to undernutrition, in particular disease-related malnutrition, which can be a result or a cause of an illness. The reasons for malnutrition are multifactorial, and its consequences may include an increased risk of pressure ulcers, reduced mobility and psychological effects such as depression. It is essential that nurses prioritise the nutritional care of all patients and identify those at risk of malnutrition using accurate and reliable nutrition screening tools. If there is a risk of malnutrition, further assessment and nutrition action planning can reduce the risk to the patient and improve their nutritional status. This article discusses the effects of disease-related malnutrition and outlines the role of screening tools and assessment in identifying patients who are malnourished or at risk of becoming malnourished. It also describes the nursing care that should be provided to patients with disease-related malnutrition, and emphasises the importance of using a multidisciplinary team approach involving speech and language therapists, dieticians, occupational therapists and physiotherapists.