The authors describe an outbreak of congenital tremor in piglets in a herd for the integrated production of fattening pigs. All sows farrowing within a period of slightly over a month gave birth to piglets affected to a varying degree. All the sows were of the Swedish Land Race and covered by boars representing two different lines not genetically related to each other. The case history comprised information on oral treatment of the sows with an antiparasitic trichlorfon compound (Neguvon) during pregnancy. Morphological examination of the CNS revealed a marked cerebellar hypoplasia in all examined piglets. Teschen/Talfan virus was isolated from liver and spleen in one of the piglets, but this finding could be repudiated as merely coincidental. It is concluded that there is strong circumstantial evidence for Neguvon treatment as a possible etiologic factor in this tremor outbreak. All relevant data collected are seen from Tables I and II.