Transthoracic fine needle aspiration cytology (TFNAC) is an invasive procedure and should therefore be subject to regular review. We report an audit of TFNAC from 146 patients. One hundred and thirty-six samples (93%) were adequate and 86 were malignant, 16 suspicious and 34 contained no malignant cells. TFNAC was the sole means of diagnosis of malignancy in 55 patients. However, further pathological data were available in 58 of the adequate samples; TFNAC was malignant in 31, suspicious in eight and contained no malignant cells in 19. All malignant TFNAC were confirmed (absolute sensitivity = 85%; positive predictive value = 100%); as were five of eight with suspicious cytology. Of 19 patients with negative TFNAC, nine were subsequently found to have a malignancy (specificity = 68%).