Epstein-Barr virus (EBV) is known to be involved in the majority of patients who develop post-transplant lymphoproliferative disorder after solid organ transplant. We conducted a retrospective study to determine the utility of qualitative and quantitative Epstein-Barr virus polymerase chain reaction (PCR) for the diagnosis and monitoring of post-transplant lymphoproliferative disorder in adult solid organ transplant patients. Peripheral blood leukocytes obtained from 35 adult solid organ transplant patients consecutively referred for evaluation of possible post-transplant lymphoproliferative disorder, were tested by EBV PCR at the time of initial evaluation and at time points thereafter. Eighteen of 35 (51%) patients were ultimately diagnosed with post-transplant lymphoproliferative disorder by tissue biopsy. Fifteen of 18 (83%) patients were found to have EBER-1 positive tumors by in situ hybridization. EBV PCR was positive in 7 of 15 patients, suggesting a sensitivity of 39%. Seventeen patients without post-transplant lymphoproliferative disorder and three with EBER-1 negative post-transplant lymphoproliferative disorder all had negative EBV PCR tests, suggesting a specificity of 100%. We observed that declines in EBV DNA load were associated with response to therapeutic interventions, such as reduction in immunosuppression, rituximab therapy and chemotherapy. We conclude that peripheral blood EBV PCR may have a role in the diagnosis and monitoring of post-transplant lymphoproliferative disorder in adult solid organ transplant patients.