Ascaris suum is the most prevalent helminth on organic pig farms (Carstensen et al., 2002) and is transmitted mainly via the faeces. The use of anthelmintics does not fit in the organic principles and preventive measures are promoted. This project focused on assessing the efficacy of a cleaning protocol for the dunging area of pens on Ascaris s. transmission to pigs. In 4 batches with 8 identical pens for 15 pigs each (n=480 pigs) 6 pigs per pen were orally infected with Ascaris s. The other pigs can be earliest infected at 10 weeks and half of the pens were thoroughly cleaned at that time. Affected livers and egg counts in the manure had to show if this cleaning protocol keeps the non infected animals free of Ascaris s. The results show no effect of the cleaning protocol on the non infected pigs. These pigs had 57% damaged livers in both treatment and 50% had positive egg counts in the manure. The conclusion is that pen hygiene does not contribute to a reduction of Ascaris s. infection