The lung and lymph node samples were collected from 786 pig farms associated with wasting and respiratory syndrome during 2005～2009. All samples were tested for the detection of porcine reproductive and respiratory syndrome virus (PRRSV) and the differentiation of its genotype using reverse transcriptase-polymerase chain reaction (RT-PCR). 643 farms (81.8%) of the pig farms examined were positive for PRRSV, of which 57.2% accounted for PRRSV type 1 and 70.2% accounted for PRRSV type 2. Furthermore, 37.5% of the farms positive for PRRSV, showed the coexistence of two genotypes. The results indicate that the PRRSV infections of single genotype or two genotypes are very common in Korean pig farms.