Immunocastration is effective to prevent sexual development and boar taint in pigs of conventional genotypes. Other studies pointed out that immunocastrated (IC) pigs show better performance than surgically castrated (SC) pigs. Apart from animal welfare aspects, this fact could be of relevance for Iberian and other fatty pig types with low lean deposition capacity. The purpose of this study was to examine the effects of immunocastration on Iberian pig performance and some carcass traits under different dietary protein concentrations. Fifty-four pure Iberian pigs were used (3 sexes: IC males, IC females, SC males; 3 isoenergetic diets: 160, 140 and 120 g CP/kg DM, 6 pigs/treatment combination). Vaccination against gonadotropin releasing factor was at 4.3 (40 kg) and 6 months of age (70-80 kg). Pigs were individually housed consuming the experimental diets from 40 to 105 kg-BW. The results indicate greater growth rate and feed conversion efficiency for IC males compared to SC males and IC females, and no relevant differences in growth related to dietary protein. Further results will help to elucidate possible effects of immunocastration on lean tissue accretion in Iberian pigs.