Purpose: Loss of chromosome 3 is strongly associated with metastasis in uveal melanoma and has been proposed as the basis for clinical prognostic testing. It is not known whether techniques that identify loss of heterozygosity for chromosome 3 predict metastasis more accurately than those that detect only numerical loss of chromosome 3 (monosomy 3). Experimental Design: Fifty-three uveal melanomas were analyzed by 28 single nucleotide polymorphisms (SNP) across chromosome 3. SNP was compared with fluorescence in situ hybridization (FISH) and array-based comparative genomic hybridization (aCGH) for metastasis prediction by sensitivity, specificity, and Kaplan-Meier survival analysts, using our validated gene expression-based classifier as a reference standard. Results: By Kaplan-Meier analysis, only the gene expression-based classifier (P = 0.001) and SNP-based detection of loss of heterozygosity for chromosome 3 (P = 0.04) were significantly associated with metastasis. Sensitivity and specificity were 95.2% and 80.8%, respectively, for SNP, 77.8% and 64.7%, respectively, for FISH, and 85.0% and 72.0%, respectively, for aCGH. Isodisomy 3 was identified by SNP but undetected by aCGH and FISH in three tumors. Conclusions: Prognostic tests based on SNP platforms, which detect both chromosomal homologues and their subregions, may be superior to techniques that only detect changes in chromosome number. These observations could have important implications for efforts to detect genetic alterations in cancer genomes with CGH-based approaches.