Congenital tremor (CT) or "shaking piglet" syndrome of newborn piglets is a well-known disease caused by different factors and resulting in different pathological alterations. In addition to non-infectious causes (like intoxication and genetic alterations), viral infections of the sow during gestation are of utmost importance. It has long time been known that classical swine fever virus, a virus belonging to the genus Pestivirus within the family Flaviviridae, induces CT. Very recently, a novel porcine pestivirus was discovered, which is also capable to induce the disease and was designated as "atypical porcine pestivirus" (APPV). APPV infection is apparently highly prevalent in pig populations worldwide. This article reviews the different forms of CT and summarizes recent studies of the newly discovered virus.