Polymerase chain reaction (PCR)-based testing is being widely implemented for diagnostic purposes. The PCR technique is generally considered to be both analytically sensitive (i.e., detects small quantities of a substance) and analytically specific (i.e., few cross reactions). There are few studies, however, of diagnostic sensitivity and specificity (i.e., the likelihood of correctly identifying infection status). The purpose of the following study was to estimate the diagnostic sensitivity and specificity, as well as the analytical sensitivity, of a RT-PCR currently being used in a midwestern diagnostic laboratory for the detection of PRRSV RNA.