Twenty five percent of orbital metastasis is usually of unknown primary origin and it requires histopathological and immunohistochemical confirmation. The fine-needle aspiration biopsy of the orbit is an alternative procedure to conventional orbitotomy. The case is presented of a 60 year-old woman with a right orbit tumour mass and neoplastic lesions in her brain and cranium. As an incidental finding, she had a thrombus in her left atrium, and so an orbitotomy procedure was ruled out. An ultrasound-guided fine-needle aspiration biopsy was performed instead with rapid on-site evaluation of biopsy samples. These showed malignant cells of a lung adenocarcinoma, which was confirmed with immunohistochemistry and chest diagnostic images. In conclusion, biopsy samples obtained by fine-needle aspiration biopsy, together with cytopathological and immunohistological analysis, enabled orbital metastasis to be identified in the case described, and showed that fine-needle aspiration biopsy is a safe, effective, and minimally invasive alternative.