The eastern focus of the current outbreak of bluetongue (BT) in the Mediterranean Basin commenced in late 1998, infecting Turkey and some of the eastern islands of Greece. In the summer of 1999 it moved to continental Greece and for the first time to Bulgaria. By the late summer of 2000, BT spread progressively through Greece and to the Balkan states. The BT virus (BTV) serotypes involved were BTV-4, BTV-9 and BTV-16. The west-central focus of the outbreak, involving BTV-2, appeared in Tunisia in December 1999 and the following summer also in Algeria. In August 2000, BTV-2 was reported for the first time in Italy (in Sardinia) and soon thereafter in France (Corsica) and in Spain (the Balearic Isles). In the autumn of 2000, a second serotype (BTV-9) emerged in southern peninsular Italy. Eventually this incursion of virus into the central Mediterranean region resulted in the largest epidemic of BT ever to affect Europe. Some features of this epidemic differ significantly from those observed previously, namely: a) its deep penetration northwards (reaching 44 degrees N both in Italy and in the Balkans) b) its persistence across four seasons in various zones of Italy and the Balkans, implying that BT could become endemic over a wide geographic area c) its successful invasion of areas separated from previously infected ones by fairly large distances (Sardinia, Sicily, Calabria, and the Balearic islands). The pattern of the spread of BT across Italy, before the introduction of vaccination, is described. The possible role of climate, soil and insect vectors on the incidence of the disease, and the overwintering of the virus, are discussed. Some hypotheses on the possible origins and modes of introduction of BTV into Italy are postulated.