Although pathogenic Yersinia have been described several decades ago, human Yersinia infections remain enigmatic. The high prevalence in Europe and the variety of manifestations should be known to most clinicians. Both Yersinia enterocolitica and Y. pseudotuberculosis may cause similar clinical pictures. The clinical spectrum encompasses both intestinal and extraintestinal infectious syndromes and reactive or postinfectious immunological manifestations. The limited value of the currently available serodiagnostic techniques and the broad clinical spectrum make reactive yersiniosis a difficult diagnosis. Yersiniosis must be considered in the differential diagnosis of rheumatic and collagen vascular diseases. In selected indications the use of newer diagnostic tools such as immunoblotting and indirect immunofluorescence may increase the diagnostic yield in idiopathic reactive manifestations or recurrent or persisting infections of unknown origin. Recently, fluoroquinolones have emerged as promising drug when therapy is indicated.