Metabolic dysfunction is an established phenomenon in people with severe mental illness (SMI), and it has a higher prevalence than in the general population. It is associated with increased morbidity and mortality, and effective recognition and management are essential to enable good psychiatric care. Despite widespread awareness of this disparity for several decades, health outcomes continue to worsen, highlighting the need for more effective preventive and treatment measures. This article outlines the risk factors that contribute to metabolic dysfunction in this population, including genetic, environmental and pharmacological factors, and considers underlying metabolic pathophysiological processes as part of SMI itself. To aid discussions with patients, recognition and interpretation of metabolic risk factors are outlined, together with mitigating strategies. Novel areas of uncertainty are discussed, including the use of a ketogenic diet. This article advocates use of the term ‘metabolic psychiatry’, to increase awareness of the significant overlap between psychiatric illness and metabolic dysfunction.