In the diagnosis of lung cancer, the cytological sample obtained during Bronchoscopy (FBS), has an increasingly important role in the characterization of malignancy. The cytological sample can be harvested during bronchoscopy by bronchial brushing, bronchial lavages or fine needle aspiration. Immunocytochemical staining allows not only to discriminate between small cell lung cancer versus non-small cell lung cancer (NSCLC), but also to identify the expression of specific markers such as TTF-1, CK7, CK20, 4A4, 34βE12 and p63. Thin Prep is a technique for cytological assay already validated and largely used in the immunocytochemical determination of gynaecologic specimens. Further Studies are required to asses the accuracy of this technique compared to conventional smear in cytological airway samples obtained by fine needle aspiration.