Toxoplasma infection is uncommon after renal transplantation. As a result, Toxoplasma gondii is often missed from the list of microbial agents which may be responsible of an infectious complication after renal transplantation. However, establishing this diagnosis is very important because toxoplasmosis can be life-threatening in an immunocompromised host, particularly when the diagnosis is too delayed. Here we report two cases of severe toxoplasmosis after renal transplantation. In the first case, primary infection transmitted by a cat developed in a seronegative recipient five years after renal transplantation. In the second case, reactivation of latent infection developed in a seropositive recipient 9 months after transplantation. In both cases, systematic screening for Toxoplasma gondii using polymerase chain reaction (PCR) in biological fluids was essential to suggest the diagnosis. Both recipients rapidly recovered after institution of antiparasitic therapy.