The relationship between placental efficiency (PLEFF, i.e., the ratio of birth weight [BWB] to placental weight [PLW]) and neonatal pig vitality as measured by the probability of preweaning death of live born piglets was examined for 1,036 live born piglets of 118 litters. The data were first analyzed to establish whether the relationships between PLEFF, PLW, and BWB were affected by parity (first vs. higher). Furthermore, the data collected were used to establish whether PLEFF is a better predictor of the risk of neonatal pig mortality before weaning than BWB and PLW. The relationships of BWB to PLW and PLEFF to PLW differed (P < 0.01 and P < 0.05, respectively) between piglets from gilts and sows. This difference appeared to be due mainly to an additional population of piglets with very large placentas in sows that were not present in gilts. Despite being significant, the courses of the relationships were essentially similar for piglets in gilts and in sows. For the curvilinear relationship of BWB to PLW, up to a certain threshold value, an increase of PLW resulted in an increase in BWB, and thereafter BWB did not change. A consequence of this is that PLEFF at relatively high PLW does not give the same