Porcine circovirus (PCV) was initially recognized as a contaminant of continuous pig kidney cell lines and was not thought to be pathogenic. Antibodies reactive to the cell culture isolate of PCV (PCV PK-15) are prevalent in the swine population worldwide. Recently, PCV PK-15-like antigen and nucleic acid were demonstrated in lesions associated with wasting syndromes in pigs in North America and Europe. Monoclonal antibodies raised to circoviruses isolated from pigs with wasting syndromes highlighted differences between these circoviruses and the PCV PK-15 cell culture isolate. This has led to speculation that a new pathogenic PCV may have emerged in the swine populations of several countries. We report the cloning and characterization of novel circovirus DNAs purified from virus isolates made from tissues of North American and European pigs with wasting syndromes. These North American and European circoviruses form a closely related group at the nucleotide sequence level (> 96% intra-group nucleotide sequence identity) but exhibit < 80% nucleotide sequence identity with the PCV PK-15 cell culture isolate. This report provides evidence for a new type of possibly pathogenic PCV. We propose that these new circoviruses should be referred to as PCV2 as opposed to the original PK-15 cell culture isolate, which should be referred to as PCV1.