Listeriosis has been a mandatorily notifiable disease in Germany since January 2001. Clinical cases with isolation of Listeria monocytogenes from sterile specimens or neonates are reported to the Robert Koch-Institut. Listeriosis incidence significantly increased from 0.26 per 100 000 inhabitants (217 cases) in 2001 to 0.62 per 100 000 (519 cases) in 2005. The increase only occurred among non pregnancy-associated cases and was mainly due to a rise in cases in the age group > or =60 years. The highest incidences were observed in neonates and adults > or =70 years. Male cases predominated, except for cases occurring in adults of child-bearing age. The overall case fatality rate was 9%. No temporal or spatial clusters of cases were observed and no outbreaks with a common source vehicle were identified. In 46% of the cases malignancies were reported as predisposing factor. Reasons for the increase of listeriosis in Germany remain unclear. The newly implemented surveillance system, and raised diagnostic awareness, cannot explain the particularly high increase in incidence from 2004 to 2005. Increased contamination of common foodstuffs or changes in underlying medical conditions or treatment options may have contributed to the increase. A project for enhanced listeriosis surveillance was begun in 2005 to obtain more detailed information about the clinical course, underlying conditions, medical treatment, knowledge about listeriosis and possible food risk factors from all newly diagnosed cases. For better outbreak detection, a nationwide system for molecular subtyping of listeria strains from humans and food is necessary. Recommendations for prevention should be extended to all risk groups with predisposing conditions