In 2001, the Dutch Dietetic Association conducted a national screening on malnutrition. The goal of this screening was to determine the prevalence of disease-related malnutrition in The Netherlands in all fields of medical care and to investigate the involvement of the dietitian in the treatment of malnutrition.Eight thousand five hundred and twenty nine patients were screened of which data of 7606 patients could be analysed. Eighty one per cent (6150) of the patients were hospital patients. Eleven per cent (808) of the patients lived in a nursing home. Seven per cent (533) of the patients were home-care patients, who were measured at home or at the general practitioner's office. The origin of 115 patients (2%) was not registered. Age, height, weight, unintentional weight loss, kind of illness and intervention by a dietitian were registered. Malnutrition was defined as >10% unintentional weight loss during the past 6 months and risk of malnutrition was defined as 5-10% unintentional weight loss during the past 6 months.Twelve per cent (884) of all patients appeared to be malnourished. Thirteen per cent (962) were at risk of malnutrition and 75% (5760) were well nourished. Fifty four per cent of the malnourished patients were referred to a dietitian. Oncological disease was more associated with malnutrition than non-oncological disease (in particular in the head and neck, lung and intestinal areas). Also, non-oncological gastro-intestinal and lung disease patients were often categorised as malnourished. Elderly patients (>75 years) were more at risk of malnutrition. BMI and unintentional weight loss did not correlate well.In this national survey conducted by dietitians, including a convenience sample of mainly institutionalised patients, approximately 25% of patients in all medical fields were categorised as moderately or severely malnourished. About half of these patients were seen by a dietitian.