Samples of superficial inguinal and bronchial lymph nodes, ileum, tonsil and lung were taken from three to five pigs on each of 61 farms with a clinical history of postweaning multisystemic wasting syndrome (PMWS). The samples were examined histologically and by immunohistochemistry for porcine circovirus type 2 (PCV-2). PMWS was diagnosed in two stages: first, an evaluation of the haematoxylin and eosinstained sections that identified the cases in which the characteristic PCV-2 cytoplasmic inclusion bodies were apparent, and secondly, a conclusive step in which immunohistochemistry was applied to confirm PMWS in the cases in which there were positive immunohistochemical results that coincided with lesions indicative of PMWS in at least one of the lymphoid and/or lung tissues. The location of PCV-2 in specific lesions (cell depletion in lymphoid organs and interstitial pneumonia) confirmed PMWS in 45 of the 61 farms, 31 of which were also infected with porcine reproductive and respiratory syndrome virus. The lymphoid tissues were more reliable than the lungs for the diagnosis of PMWS, both in individual pigs and in groups of pigs, and farm diagnoses based on a group of pigs were more reliable than diagnoses based on single pigs.