Adult-to-adult living donor liver transplantation (ALDLT) using small-for-size grafts (SFSGs), ie, a graft with a graft-to-recipient weight ratio (GRWR) <0.8%, has been a challenge that should be carefully dealt with, and risk factors in this category are unclear. Therefore, we aimed to examine the risk factors and outcomes of ALDLT using SFSGs over a 13-year period in 121 patients who had undergone their first ALDLT using SFSGs. Small-for-size syndrome (SFSS), early graft loss, and 1-year mortality were encountered in 21.6%, 14.9%, and 18.4% of patients, respectively. By multivariate analysis, older donor age (≥45 years) was an independent risk factor for SFSS (odds ratio [OR], 4.46; P = 0.004), early graft loss (OR, 4.11; P = 0.02), and 1-year mortality (OR, 3.76; P = 0.02). Child-Pugh C class recipients were associated with a higher risk of SFSS development (P = 0.013; OR, 7.44). Despite no significant difference between GRWR categories in the multivariate outcome analysis of the whole population, in the survival analysis of the 2 donor age groups, GRWR <0.6% was associated with significantly lower 1-year survival than the other GRWR categories in the younger donor group. Moreover, in the high final portal venous pressure (PVP) group (>15 mm Hg), younger ABO-compatible donors showed 100% 1-year survival with a significant difference from the group of other donors. Older donor age was an independent risk factor for SFSS, early graft loss, and 1-year mortality after ALDLT using SFSGs. GRWR should not be <0.6%, and PVP modulation is indicated when grafts from older or ABO-incompatible donors are used.