Pinworm Enterobius spp. has probably been an endemic parasite in humans in Iceland since the colonization of the country more than 1100 years ago. A recent survey on pinworm infections in children in playschools indicated that the pinworm is quite common. The results are published in another article in this issue. In this contribution general knowledge on the biology of the parasite (taxonomy, morphology, distribution, life-cycle, transmission, diagnosis and treatment) is reviewed. Recently, dozens of male pinworms found in a stool sample were identified as Enterobius gregorii. Since no other species identifications have been made in Iceland so far, it is not known if the other pinworm species E. vermicularis also occurs in Iceland.