Prior to the introduction of porcine circovirus vaccines, losses from porcine circovirus type 2 infection were high on many Ontario farms. A survey of swine health experts revealed that a large number of intervention strategies were being recommended but generally with disappointing results. A field trial was performed to evaluate a new vaccine (Porcilis Circo inac ®). The mortality risk in both the vaccinated and control group (1.5% and 4.5%, respectively) was reduced compared to historical controls. The vaccine caused the pigs to produce an antibody response and provided protection from clinical disease due to porcine circovirus infection and reduced viremia based on polymerase chain reaction testing. Hematology and blood biochemistry parameters of pigs showing clinical signs of porcine circovirus infection demonstrated a lymphopenia in 3 of 4 cases but in general peripheral blood changes might not be useful in a diagnostic work-up for porcine circovirus associated diseases.