The roundworm Ascaris suum is a highly prevalent intestinal parasite of pigs worldwide, and the infection may have low to moderate pathogenic effects on health and productivity. Besides these direct effects, there may be indirect effects on enhanced susceptibility or pathogenicity to bacterial or viral infections, related to the migratory and immune-modulatory capacity of A. suum. Losses due to ascariasis in pigs can thus be summarized as (1) farm economic losses due to clinical effects (although limited), reduced growth and feed conversion efficiency and costs of control (e.g. use of anthelmintics), (2) abattoir operator losses due to condemnation or downgrading of livers and lower product quality, and (3) potential interference with vaccinations and higher risk of co-infections. Apart from the cost of liver condemnations that can be extrapolated from available data, it is difficult to quantify losses. © 2013