BACKGROUND & AIMS Detection and notification of malnutrition are essential to adopt a support plan and take costs into account. The aim of this study was to describe how often discharge sheets from Internal Medicine (IM) units include malnutrition among diagnoses (notification frequency) using the International Classification of Diseases, 9th Revision Clinical Modification -ICD-9. Factors associated with this diagnosis and its prognostic implications are also assessed. MATERIAL AND METHODS The Minimum Basic Data Set from the Spanish hospitals (Ministry of Health and Consumer Affairs) was revised, and patients with diagnosis of malnutrition (ICD-9: 260-263.9) were identified. RESULTS 1,567,659 patients were analysed (21,804-1.4%- with malnutrition). These patients were older (72.4 vs 70.8 years of age), had a greater degree of comorbidity (Charlson >2: 28% vs 23.5%), and resided in nursing homes more often (3.9% vs 1.9%) than the non-undernourished. The malnutrition associated diagnoses were: dementia, cancer, HIV infection and chronic renal failure. Mortality (19.5% vs 9.8%), hospital stay (18.1 vs 9.8 days), costs (5228.46 vs 3537.8 €) and relative weights applied to each Diagnosis Related Group (2.6 vs 1.1) were higher (p < 0.001 for all comparisons). CONCLUSIONS Notification of malnutrition in IM departments is low, below the prevalence described in inpatients. This diagnosis is associated with an increase in morbidity, mortality and costs.