In a retrospective study (1984-1992), new cases of human echinococcosis were registered in Switzerland based on information obtained from (a) questionnaires sent to 294 of the 300 acute hospitals in all parts of the country and to 17 institutes of pathology (268 answers form hospitals: 91%), and (b) from tracing back cases reported under the official notification system since 1 January 1988 by laboratories to the Federal Health Office or recorded at the Institute of Parasitology in Zurich. Cases were regarded as verified if the diagnosis was documented by unequivocal findings (by radiology, ultrasonography, pathomorphology etc. and often by additional detection of anti-Echinococcus antibodies). Patients with antibodies but without reports on further findings were classified as suspected cases. From 1984 to 1992 (9 years), 302 new cases of human echinococcosis were diagnosed in Switzerland and verified in this study, corresponding to an annual average of 34 new cases and a range between 26 and 43 cases. The total number of 302 cases included 228 (75%) of cystic echinococcosis (CE) (Echinococcus granulosus), 65 (22%) of alveolar echinococcosis (AE) (E. multilocularis), and 9 (3%) of non-specified echinococcosis (NSE) (Echinococcus sp.). Among 185 patients with CE and 60 patients with AE and known geographic origin, the ratio of Swiss nationals to foreigners was 25%:75% and 88%:12% respectively. Based on a total population (Swiss nationals and foreigners) of 6.62 million in 1988 and the case numbers of 1984-1992, the following average annual incidence rates per 100,000 inhabitants were calculated: 0.51 for all new cases, 0.38 for CE, 0.11 for AE and 0.01 for NSE. In the 37 years since 1956 there has been steady increase in new cases of CE due to the importation of such cases by foreigners, whereas the case numbers of AE have remained nearly constant with a range between 7 and 10 new cases per year. In our study 258 suspected seropositive patients were registered but not added to the total number of cases, due to the lack of further findings.