Botulism in humans is caused by botulinum neurotoxins, produced in most cases by Clostridium botulinum, although other Clostridia species are implicated as well. Of the five forms of botulism in humans, three are referred to as "infective": wound botulism, infant botulism, and adult intestinal botulism; the latter two forms are also referred to as "intestinal toxemia botulism" because the organism colonizes the lumen of the intestinal tract and produces botulinum neurotoxin in vivo. Twenty-three cases of infant botulism and three cases of adult intestinal botulism occurred in Italy between 1984 and 2005. Microbiological analyses of clinical, environmental, and food samples and analysis of clinical and epidemiological data revealed two main characteristics of intestinal toxemia botulism in Italy that are not common in cases in other countries: the isolation of a strain of C. butyricum that produced botulinum neurotoxin type E in 6 of 26 cases, including two cases of adult intestinal toxemia botulism, and the onset of botulism in these cases with concomitant severe gastrointestinal symptomatology. This report summarizes the microbiological, clinical, and epidemiological data of all cases of intestinal toxemia botulism that have occurred in Italy in the period 1984-2005.