Two outbreaks of porcine parvovirus occurred in a unit of 380 sows, with a subsequent decrease in the size of gilts' litters. Of the 203 gilts and 64 primiparous sows which were seronegative at the time of insemination, 134 gilts and 55 primiparous sows seroconverted during pregnancy. Of the second parity sows nine of 271 were still seronegative at the time of insemination but all nine seroconverted during their third gestation. The gilts that seroconverted during their first pregnancy produced on average 0.9 fewer live piglets than the gilts that did not seroconvert. Second litter sows which seroconverted produced 0.3 fewer piglets than those which did not seroconvert. There were no significant differences between sows which seroconverted or did not seroconvert in the numbers of returns to service, or in the percentages of piglets which were born dead or died before weaning.