In this study, the prevalence of PMWS affected pigs was determined in three Belgian farms with a history of PMWS and in four control farms with no suspicion of PMWS. The diagnosis of PMWS was based on the fulfillment of all four of the following criteria: the presence of wasting, gross lesions and histopathological lesions suggestive of PMWS and the presence of high PCV2 titers in the lymphoid organs. In the farms with a history of PMWS, 2% of the piglets died of PMWS during the observation period. In the control farms, 0.1% of the piglets were found to be affected with PMWS. Serological examinations showed that all piglets became infected with PCV2 on all farms and no differences in serological profiles were seen between farms or litters with or without PMWS-affected piglets. PRRSV infections were clearly demonstrated in PMWS-affected and non-affected piglets but no correlation was seen between simultaneous infections with PCV2 and PRRSV and the occurrence of PMWS.