Malnutrition is a frequent problem for hospitalized patients. It is a relevant risk factor for morbidity and mortality. The aim of this study was to detect undernutrition and the risk of malnutrition (RM) in patients admitted to a university-affiliated respiratory care clinic. Undernutrition was assessed by body mass index (BMI<18.5 kg/m²) and RM by using the "Nutritional Risk Screening 2002" (NRS 2002) in 705 consecutive patients (BMI: measured in 689 patients/NRS: 680 patients assessed). Data was analysed with regard to age, sex, length of hospital stay as well as underlying pneumological disorders. In 14.3% of 680 patients, RM was detected by NRS. In 2.5% out of 689 patients, undernutrition was identified by BMI. In patients older than 65 years (n=365), these numbers were 19.6% (NRS) and 1.5% (BMI<18.5 kg/m²). Age was a significant risk factor for RM (OR 1.054 per year). Gender, however, was not associated with undernutrition or RM. In a sub-analysis, RM was more frequent in patients with pneumonia and chronic obstructive lung disease (23% and 16%, respectively). Patients with cancer were more frequently at RM as compared to patients with sleep-disordered breathing (OR: 2.33 in cancer, OR: 0.04 in sleep-disordered breathing). RM was associated with a significant increase in length of hospital stay (10.2 ± 9.5 vs. 5.4 ± 6.0 days). Besides the BMI, the NRS provides a valid tool for screening patients at RM.