Investigations were performed to characterize porcine circovirus (PCV) 2 infection in 10week old pigs from a case of apparent vaccine failure. Thirty serum samples were collected from affected or non-affected pigs and tested for anti-PCV2 antibodies and PCV2 DNA. To address potential PCV2 vaccine compliance issues, samples were tested for antibodies against baculovirus and Mycoplasma hyopneumoniae antigens present in the PCV2 vaccine utilized in this herd. Both PCV2a and PCV2b DNA were detected in 76.6% (90% positive for PCV2a, 86.6% positive for PCV2b), anti-PCV2 IgG in 90%, anti-baculovirus IgG in 50%, and anti-M. hyopneumoniae IgG in 43.3% of the samples. Frequency of baculovirus and M. hyopneumoniae seropositive pigs was significantly lower in affected pigs. The finding that only 50% of the pigs developed a detectable immune response to vaccination suggests poor vaccine compliance or efficacy. Concurrent PCV2a and PCV2b infection was common and may have resulted in enhanced PCV2 replication.