Purpose To analyse in vivo structural and cellular features of ocular surface squamous neoplasia using clinical confocal microscopy. Methods Ten consecutive cases of untreated ocular surface squamous neoplasia were in vivo investigated using clinical confocal microscopy (ConfoScan4, Nidek Co. Ltd, Gamagori, Japan) with a  40 surface non-contact objective lens. Confocal microscopy images were compared with cytologic samples obtained by scraping technique. Results Confocal microscopy examination revealed large areas of superficial cells debris and/or keratin debris accompanied by syncytial-like groupings, loss of the normal structure of the conjunctival epithelium and\or of the corneal basal epithelium layer, papillomatous organization, large fibrovascular structures, and fine vessels perpendicular to the tumour surface. Sub-epithelial (pre-Bowman) space involvement was documented in four cases (50%). Irregular healthy tissue infiltration at the lateral edge of the lesion was documented in two cases (20%) whereas abrupt demarcation between neoplastic cells and normal epithelium was documented in eight cases (80%). In vivo cyto-morphologic study using clinical confocal microscopy showed cellular anisocytosis, pleocytosis, and anisonucleosis, enlarged nuclei with high nuclear to cytoplasmic ratio, high reflective cytoplasm and indistinct cytoplasmic borders in all cases (100%). Conclusion CCM appears to be a promising and non-invasive method for in vivo structural and cellular analysis of OSSN.