The ideal method for obtaining lung tissue for diagnosis should provide high diagnostic yield with low morbidity and mortality. We reviewed all 432 patients (mean age 55 years) who underwent an open lung biopsy at this hospital over a 10-year period. Twenty-four patients (5.5%) were immunocompromised. One hundred and twenty-five patients were on steroid therapy at the time of operation. Open lung biopsy provided a firm diagnosis in 410 cases overall (94.9%) and in 20 out of 24 patients in the immunocompromised group (83.3%). The commonest diagnosis was cryptogenic fibrosing alveolitis (173 patients). Twenty-two patients (5.1%) suffered complications following the procedure: wound infection 11 patients, pneumothorax 9 patients and haemothorax 1 patient. Thirteen patients (3.0%) died following open lung biopsy, but in only 1 patient was the death attributable to the procedure itself. We conclude that open lung biopsy is an accurate and safe method for establishing a diagnosis in diffuse lung disease with a high yield and minimal risk.