BACKGROUND In patients with severe chronic obstructive pulmonary disease (COPD), anaemia is common and associated with impaired long-term survival and quality of life. Whether anaemia is also prevalent in patients with other severe, non-inflammatory respiratory diseases has not yet been systematically tested. METHODS In 595 patients with obstructive (OD, 54.8%) or restrictive disease (RD, 45.2%) and chronic respiratory failure (CRF), anthropometric data, laboratory parameters, lung function, blood gases and comorbidities were assessed prior to initiation of home mechanical ventilation. Patients were classified as anaemic based on haemoglobin (Hb) levels (Hb<12/13 g/dl, female patients/male patients). Patients with known causes for anaemia were excluded. RESULTS In patients with CRF the prevalence of anaemia was 13.3% and not different between RD (11.5%) and OD (14.7%) (p=0.276). A sex-related difference occurred only in OD [7.9% (f) vs. 17.3% (m); p=0.035]. Patients with OD and anaemia presented with higher age (p=0.003), pH (p=0.014) and arterial oxygen pressure (PaO(2) ) (p=0.012), lower body mass index (BMI) (p=0.011) and total protein (p=0.012) and higher rates of coronary heart disease (p=0.01), cardiac arrhythmia (p=0.014) and diabetes mellitus (p=0.003) in comparison to non-anaemic patients. In patients with RD anaemia was associated with higher age, (p=0.008), pH (p=0.011) and lower leucocytes numbers (p=0.006). CONCLUSIONS Anaemia is frequent not only in COPD but also in other severe respiratory diseases combined with CRF. It was associated with advanced age, several comorbidities, impaired nutritional state and elevations of pH and PaO(2) , probably because of hyperventilation. Its prognostic impact has to be elucidated in future studies.