The diagnosis may be made on sputum cytology and is more successful if taken as early morning specimens on successive days. Chest x-ray will usually show a hilar mass in the presence of a central tumour or a spiculated peripheral mass. Obstructive pneumonitis and a pleural effusion may also be evident.

Bronchoscopy is essential to biopsy any central tumour, take bronchial washings from the site of a peripheral lesion and to exclude other endobronchial disease.