BACKGROUND: Uveal melanoma (UM) can be classified by tumour size category and by The Cancer Genome Atlas (TCGA) groups (cytogenetic-based, 4-category prognostic classification into Groups A-D). This study was conducted to assess impact on metastasis-free survival (MFS) in UM by tumour size category based on correlation with TCGA classification. METHODS: Retrospective analysis of 1002 cases categorised as small (0.0-3.0 mm), medium (3.1-8.0 mm) and large (≥8.1 mm), grouped by TCGA classification. RESULTS: Of 1002 cases, TCGA Groups (A/B/C/D) included small (n = 270, 75%/11%/13%/1%), medium (n = 503, 46%/14%/27%/13%) and large (n = 228, 23%/19%/38%/20%) UM. The 5-and 10-year Kaplan-Meier MFS for small UM revealed Group A (98%, 98%), Group B (100%, 100%), Group C (86%, NA) and Group D (100%, NA). For medium UM, the values dropped with Group A (95%, 93%), Group B (90%, 90%), Group C (68%, 38%), and Group D (44%, NA). For large UM, the values dropped further with Group A (94%, 86%), Group B (85%, NA), Group C (40%, 28%), and Group D (23%, NA). Additionally, a comparison (small vs. medium vs. large tumour size category) revealed TCGA low-risk grouping (Groups A or B) in 86% vs. 60% vs. 58% cases with UM. CONCLUSION: By tumour size category, favourable cytogenetics (Groups A or B) is found in 86% of small tumours, 60% of medium tumours, and 58% of large tumours. The MFS at 10 years for favourable cytogenetics was 98% for small tumours, 92% for medium tumours, and 54% for large tumours. Tumour size category can serve as a surrogate for TCGA.