Though transthoracic needle biopsy (TNAB) is a well established method for obtaining pathologic diagnosis in lung masses, very often the procedure is only performed after a previous negative bronchoscopic biopsy (BB) attempt. In this study we analyzed the results of TNAB in 129 consecutive patients where one or more inconclusive BB had been performed. TNAB was diagnostic in 115 of 129 lesions (89%) and the yield was not significantly affected by size, cell type or tumour location. In 97 patients who underwent thoracotomy, cytologic specimens obtained by TNAB accurately reflected histologic tumour type in all cases. A false negative rate for malignancy on TNAB was 5%. Awaiting inconclusive BB results caused an average delay of three in-hospital days before TNAB. In those patients in whom a biopsy is warranted, TNAB is most useful as an initial diagnostic procedure in masses that are peripheral and in pleural based tumours, in mediastinal adenopathy associated with a lung mass and instead of a repeat, previously failed bronchoscopy.