In a 3-year prospective study, all cases of disseminated Fusobacterium necrophorum infections found in Denmark from 1998 to 2001 were analysed, with the aim of describing the epidemiology and clinical features of the variants of Lemierre's syndrome and disseminated non-head-and-neck-associated F. necrophorum infections. Fifty-eight cases of Lemierre's syndrome were reported in previously healthy persons, with an incidence of 14.4 cases per million per year in youngsters aged 15-24 years old. There was no increase during the study period. Lemierre's syndrome originating from an oropharyngeal infection was seen in 37 youngsters. An otogenic variant of Lemierre's syndrome was seen in 5 children with dissemination to nearby regions, and other variants of Lemierre's syndrome, e.g. from the sinuses and teeth, were seen in 16 adults. Patients often had metastatic infections already on admission and needed prolonged hospitalisation. The overall mortality of Lemierre's syndrome was 9%. Forty-two elderly patients had disseminated F. necrophorum infections originating from foci in lower parts of the body. They frequently had predisposing diseases, e.g. abdominal or urogenital cancers, which contributed to the high mortality of 26%. This study shows that the incidence of Lemierre's syndrome is higher than that previously found and has a characteristic age distribution. Early suspicion of the diagnosis, several weeks of antibiotic therapy, often combined with surgical drainage, is mandatory to lower the mortality. In disseminated non-head-and-neck-associated F. necrophorum infections, underlying cancers must be considered.