Post-transplant lymphoproliferative disorders (PTLDs) are a heterogeneous group of lymphoid neoplasms associated with immunosuppression following transplantation. Among PTLDs, monomorphic PTLD (m-PTLD) is the largest category; however, its characteristics and survival outcome are not fully understood because of low incidence. This study enrolled 30 adult patients with m-PTLD after kidney-transplantation (KT, n = 17) and hematopoietic stem cell transplantation (HSCT, n = 13) from January 1998 to December 2014. The incidence rates of m-PTLD were 0.74 and 3.63% in the KT and HSCT groups, respectively. M-PTLD patients in the HSCT group were younger and showed earlier onset, with EBV-encoded small RNAs (EBER) more frequently identified. Diffuse large B cell lymphoma (DLBCL) was the main pathological type, and the digestive system was the most extranodal involvement site in m-PTLD after KT and HSCT. Among the 28 patients with DLBCL m-PTLD,the complete remission rate after rituximab treatment was higher than in patients not administered rituximab treatment (P = 0.038). With a median follow-up of 46 months after m-PTLD diagnosis, the estimated 5-year overall survival (OS) was 59.2 +/- 9.1% in all patients, and 64.2 +/- 11.8 and 52.7 +/- 14.1% in the KT and HSCT groups, respectively (P = 0.741). ECOG PS, Ann Arbor stage, and CD68 IHC expression were independent prognostic factors for OS. M-PTLD is a rare but serious complication after transplantation. Ongoing efforts to standardize safe and effective treatment protocols would improve the poor overall survival. The independent prognostic factors contributed to risk-stratified treatment, and might be validated by larger studies.