Piglet mortality before weaning is an important cause of economic loss in the pig production. Most pigletmortality occurs during the first four days after birth, and the major part is caused by non-infectious conditions. Thecauses can be found in the sow, the piglets as well as in the environment. This article gives a review of the mostimportant causes related to the sow or the environment. Regarding sow factors, emphasis is placed on lactationproblems, aggression, parity of the sow and litter size. Concerning the environment, the effect of temperature, traumaand poor herd health management are discussed.