Three strains of Shigella dysenteriae type 2 were isolated from a small household outbreak which occurred in Palermo, Sicily, during summer 1990. Two isolates were recovered from hospitalized patients and one from an asymptomatic carrier. The infection could not be associated with travel to foreign countries or contact with travellers returned from abroad. Since 1953 S. dysenteriae has been never isolated in Southern Italy. The isolates from dysentery cases were susceptible to antibiotics and carried a plasmid of 120 MDa associated with a small cryptic plasmid; in contrast, the strain isolated from the healthy carrier contained an additional plasmid of approximately 40 MDa, which codified for resistance to ampicillin, streptomycin, sulfamethoxazole and trimethoprim. All strains showed some atypical biochemical properties, but their rRNA-DNA patterns of hybridization were closely similar to that of the reference strains of type 2 and easily distinguishable from those of the other types of non-Shiga bacillus reference strains. Epidemiological isolation features of these strains suggest a possible circulation of this Shigella species in Sicily. Genetic characterization of these strains may be useful for surveillance of infections by this organism.