Leptin is an adipocyte derived hormone and correlates highly to the extent of body fat tissue. The aim of this study was to determine if leptin could serve as an early predictor for carcass composition and final growth rate in lambs with special emphasis on size and cellularity of the different body fat depots. Thirty intact male ad libitum fed lambs were blood sampled at 20, 25, 30, 35, and 40kg live weight. After slaughtering at 40kg, lean and the visceral, subcutaneous and intermuscular fat were measured by dissection. The fat cell diameter was determined in subcutaneous and perirenal fat. Average daily gain from birth to slaughter correlated to leptin only at 30 and 35kg live weight (r=-0.56 and -0.61, P<0.01) and thus leptin cannot be regarded as a suitable early predictor for growth rate. That goes for the prediction of subcutaneous and intermuscular fat, too; because no relationships were detected between early leptin concentrations and the amount of these tissues. Leptin concentrations measured just before slaughter were related to all fat tissues except the pelvic and intramuscular fat. Among the visceral fat depots, omental fat expressed the highest correlations to leptin (r=0.60, P<0.001). Additionally, leptin concentrations at 35 and 40kg live weight increased with increasing fat cell diameters (r=0.38, P<0.05 to r=0.59, P<0.001). This study indicates that leptin concentration measured in the slaughter weight range has the greatest potential to assess body fat content, whereas an earlier prediction does not seem to be feasible. Further studies should clarify if these results are reproducible for other breeds or species.