Description: Canine leptospirosis is a well known zoonotic infection with worldwide distribution. The serovars Canicola and Icterohaemorrhagiae have traditionally been responsible for most cases of canine leptospiroses. The use of widely available bivalent vaccines containing those two serovars has greatly reduced canine leptospirosis. However, re-emergence of the disease has been detected in Europe and North America, partly due to changes in the infecting serovars. The aim of this study was to determine the prevalence of the presumed infective serovars in dogs in Croatia. During a period of four years (2006-2010), 151 canine sera were submitted to the Laboratory for Leptospires, Faculty of Veterinary Medicine, University of Zagreb. Using a microscopic agglutination test (MAT), 57 (37.7 percentage) seropositive sera were detected. The most prevalent presumed infective serovars, in decreasing order, were: Pomona, Grippotyphosa, Icterohaemorrhagiae, Australis, Saxkoebing and Hardjo. Results showed that most infections were caused by serovars not covered by the vaccine, which raises questions concerning its efficacy in preventing leptospirosis in dogs