Introduction: Too small or too big liver grafts for recipient's size has detrimental effects on transplant outcomes. Research Questions: The purpose was to correlate donor-recipient body surface area (BSA) ratio or BSA index (BSAi) with recipient survival, graft survival, hepatic artery or portal vein, or vena cava thrombosis. High and low BSAi cut-off points were determined. Design: There were 11,245 adult recipients of first deceased donor whole liver-only grafts performed in the UK from January 2000 until June 2020. The transplants were grouped according to the BSAi and compared to complications, graft and recipient survival. Results: The BSAi ranged from 0.491 to 1.691 with a median of 0.988. The BSAi > 1.3 was associated with a higher rate of portal vein thrombosis within the first 3 months (5.5%). This risk was higher than size-matched transplants (OR: 2.878, 95% CI: 1.292-6.409, P = 0.01). Overall graft survival was worse in transplants with BSAi ≤ 0.85 (HR: 1.254, 95% CI: 1.051-1.497, P = 0.012) or BSAi > 1.4 (HR: 3.704, 95% CI: 2.029-6.762, P 1.4. These findings were confirmed by bootstrap internal validation. No statistically significant differences were detected for hepatic artery thrombosis, occlusion of hepatic veins/inferior vena cava or recipient survival. Conclusions: Donor-recipient size mismatch affects the rates of portal vein thrombosis within the first 3 months and overall graft survival in deceased-donor liver transplants
