Post-transplant lymphoproliferative disorders (PTLDs) represent a serious complication in solid organ transplantation and are the first cause of cancer related mortality in this population. Pre-transplant Epstein Barr Virus seronegativity and receipt of T cell depleting agents for induction or severe/refractory rejection are known risk factors, but they primarily impact early occurring disease. On the other hand, late occurring disease, which has typically not correlated with the above or other specific risk factors, has recently been shown to be associated with older recipient age and prolonged receipt of calcineurin inhibitors. Furthermore, recent data has contributed to and, in some instances shed light on, previous debate concerning the role of viruses other than EBV and the level of HLA mismatches as risk factors for PTLD. Gene association studies focusing on key cytokines and their receptors have identified several polymorphisms that may prove useful to identify patients at risk, with distinction for early and late occurring disease. Determining the influence of individual maintenance immunosuppressive agents on lymphomagenesis has been limited by the complexity of the multi-drug regimens used and absence of measures of drug exposure and time-dependent covariates in multivariable analyses. Biomarkers that measure the extent of immunosupression may have a role in avoiding PTLD, and other post-transplant complications.