Uveal melanoma (UM) is the most common form of primary eye cancer. The incidence of UM in the United States is approximately 4.3 cases per million. UM is more common in older individuals, with incidence rates peaking at age 70, and is associated with characteristics such as fair skin and eye color. UM affects the iris, ciliary body, and choroid portions of the uveal tract, the middle of the three concentric layers of the eye. The choroid is the most common site of UM origin while the iris is the least common site. Melanomas located near the back of the uveal tract (choroid portion) are detected later, are associated with more malignancy, and are more likely to metastasize. Metastatic disease is rarely found at the time of diagnosis, but fatal liver metastasis is common and develops within 15 years in approximately half of UM patients. Removal of the eye was the standard treatment for UM in the past, and is still sometimes performed when tumors are large. More recently, eye-sparing therapies such as tumor removal and radiation have become preferred. In many cases the primary tumor can be effectively treated with these methods. Despite advances in treatment and improvement of diagnostic methods, however, there has been no corresponding improvement in patient survival. There are numerous factors, such as tumor size and cancer cell type, that are associated with a poor outcome in UM, but none of these is accurate enough to use in making clinical decisions for individual patients. Large-scale genetic alterations, such as the presence of only one copy of chromosome 3 (monosomy 3), have been reported in UM and have been associated with metastatic disease. Recent research using a type of genetic testing called gene expression profiling has suggested that tumors can be sorted into two classes with different characteristics and prognosis: class 1 tumors are thought to be at lower risk for metastasis, while class 2 tumors may be at high risk.