This thesis presents the author's experience with diagnostic intraocular fine needle aspiration biopsy in 18 patients with a suspected metastatic choroidal or ciliary body tumor. The author has reviewed the literature on biopsy of intraocular tumors and has specified what he believes to be valid indications for diagnostic biopsy of posterior uveal tumors. He has evaluated the accuracy, limitations, and complications of diagnostic fine needle aspiration biopsy in this series and others, and he has suggested methods for improving the recovery of sufficient cells for cytologic diagnosis and lessening the risks of tumor cell seeding during the biopsy. The author has concluded that fine needle aspiration biopsy appears to be a relatively safe, generally reliable means of establishing the pathologic diagnosis of a choroidal or ciliary body tumor in highly selected patients suspected of having metastatic cancer. In spite of its apparent safety and reliability, however, the author has cautioned against the routine use of fine needle aspiration biopsy in patients with posterior uveal tumors since its long-term safety has not been established. The author has suggested that diagnostic fine needle aspiration biopsy of posterior uveal tumors be performed only in medical centers where there can be input from and cooperation among ophthalmologists, ophthalmic pathologists, and cytopathologists who are experienced in the diagnosis of intraocular malignancies.