Lawsonia (L.) intracellularis is the etiologic agent of ileitis, which occurs in different forms in pigs. The infection can be demonstrated by several methods. In routine diagnosis the indirect detection of L. intracellularis is conducted by measuring antibodies performing an indirect IFT or ELISA. Furthermore, an IFT and PCR on faecal and/or tissue samples are well established for the direct detection. The suitability of PCR on faecal samples is frequently discussed. Problems are related to various inhibitors that are component of faeces. When interpreting laboratory results, the past medical history of pigs, i.e. antimicrobial treatment, has to be considered. Since 2004 a new vaccine against ileitis is licensed. A possible influence of vaccination on diagnostic testing, especially PCR and ELISA, is hardly investigated. Therefore, the interpretation of laboratory results from vaccinated animals is, considering the current literature, restrained.