Background: Various studies have demonstrated an increased risk for adult diseases in newborns born small-for-gestational-age (SGA). Adiponectin and resistin can be detected in cord blood and are suggested to affect insulin resistance (IR). This might represent a link between metabolic syndrome and SGA birth. Study Design: We investigated the relationship between the adipocytokines and inter-twin birth weight (BW) difference of 31 monozygotic twins with twin-twin transfusion syndrome; in 14 twin pairs BW difference was >15% (1 SGA twin, 1 appropriate-for-gestational-age, AGA, twin). Results: BW and length of all patients were positively related to adiponectin (r = 0.57; p < 0.0001; r = 0.47; p < 0.0001) and to resistin (r = 0.31; p < 0.01; r = 0.35; p < 0.01). In 71% (10/14), the SGA twins showed lower adiponectin concentrations than their AGA co-twins (only 6/14 for resistin). To correct for gestational age we calculated the relationship between the intrapair differences (Δ) of BW and Δ of the hormones. We found ΔBW positively correlated with adiponectin (r = 0.55; p < 0.001) but not with resistin (r = 0.22; p = 0.2). Δadiponectin was positively correlated with Δresistin (r = 0.45; p < 0.01). Conclusion: These data demonstrate that adiponectin and resistin levels are associated with BW with only adiponectin levels being reduced in SGA children independently of gestational age. Prenatally different metabolic status between the twins might predispose the SGA twin to develop IR later in life.