The annual numbers of reports of listeriosis in England, Wales and Northern Ireland received by the PHLS Communicable Disease Surveillance Centre (CDSC) and the Division of Microbiological Reagents (DMR) have shown remarkable changes in recent years. There was a near doubling in 1987 compared to 1986; a further increase in 1988; a sharp decline in 1989 (which occurred in the second half of that year) and, finally, the total in 1990 was the lowest since 1984. The rise and fall particularly (but not exclusively) involved pregnancy-associated cases and illness caused by serotype 4. The epidemiological and clinical features reported in 1990 were otherwise similar to those reported in previous years and in other countries. Patients with the non pregnancy-associated (also called 'adult/juvenile') type were in the majority, most of whom had an underlying disorder associated with impaired immunity. The reason for the changes in reported incidence is not completely understood but is probably due to the emergence and disappearance of a common food source of the organism. There is, however, no cause for complacency. Diagnostic vigilance must be maintained and vulnerable groups should adhere to existing dietary advice.