Abstract The Eastern cottontail, a lagomorph native to the American continent, was introduced to N-Italy in the mid-1960s. In subsequent years a rapid territorial expansion and a remarkable demographic increase has been observed in many areas. In the province of Alessandria, NW Italy, we used night-time censuses with spotlights and road mortality assessment to evaluate the diffusion of the species and its trend. Night-time censuses were performed each year in spring and in autumn along 51 transects which were 10 km long on average. Road deaths were extracted from our 6715 records regarding 85 species of mammals, birds and reptiles found dead along the roads. The distribution area expanded markedly from the 1980s, and the expansion persisted between 1996 and 1997, while in 1998 the area failed to increase further, settling at around 620-660 km². The species is not present, at the moment, in the entire Apennine sector nor in the eastern and southern plains. The densities reach maximum values of 2.5-2.75 individuals/10 ha. From the road-death data we found a progressive increase of the Eastern cottontail, its proportion of the total mammals rising from 2.2% in 1995 to 3.7% in 1996 and 6.0% in 1997.