Progressive involuntary weight loss, in particular the loss of lean tissue, is common in patients with advanced cancer and has long been recognised to result in a deterioration in performance status and quality of life, increased morbidity and mortality. The aetiology of such weight loss or cachexia is complex and involves both tumour and host responses. Thus, identification of patients who are or are likely to become cachectic has been problematic. In addition to a reduction in appetite and increased satiety leading to poor dietary intake, there is now increasing clinical evidence that the activation of a chronic ongoing systemic inflammatory response is one of the earliest and most important contributory factors to cachexia. Such findings help to explain the failure of simple nutritional programmes to reverse weight loss adequately in patients with cancer. In the present paper the development of an inflammation-based score is described, which is derived from the acute-phase proteins C-reactive protein and albumin and is termed the Glasgow prognostic score (GPS). Its value as a predictor of survival, independent of tumour stage, performance status and treatment (active or palliative), has been shown in a variety of advanced common solid tumours. The nature of the relationship between the GPS, appetite, body composition, performance status and quality of life of the patient with advanced cancer will be described. Recently, it has become evident that the systemic inflammatory response is also present in a smaller proportion of patients with primary operable cancer and is also predictive of disease progression and poor survival. The role of GPS in clinical decision making will be discussed.