In a Swiss dairy farm (canton of Geneva) consisting of 73 animals 8 abortions were observed within 2 weeks. Serological and molecular biological analyses (PCR) on aborting dams, and abortion materials, respectively, revealed that the protozoan parasite Neospora caninum was the causative agent. Besides the 8 aborting animals, 12 other non-aborting heifers were found to be serologically positive for this parasite. All positive sera were further tested in an avidity-ELISA to elucidate the recency of infection. All seropositive animals but one showed low avidities at the time the abortion storm started. This indicated at a recent N. caninum-infection within the herd. Thus, the animals most probably were exposed to N. caninum-oocysts (e.g. by dog feces-contaminated forage) and the resulting abortion storm was due to an exogenous (formerly known as "horizontal") parasite transmission into a naive herd. This is the first documented record of such an event in Switzerland.