Aim: To develop a pharmacovigilance program of calcineurin inhibitors used in pediatric renal and liver transplant patients at Hospital de Pediatria JP Garrahan, Argentina. Methods: Adverse drug reactions (ADRs) of pediatric patients with kidney and liver transplantation treated with calcineurin inhibitors (cyclosporine and tacrolimus) were evaluated by retrospective review of medical records of patients transplanted between 2010 and 2011. In addition, we carried out active pharmacovigilance since March, 2011. ADRs were reported to the National Health Authority. Results: A total of 59 patients, 28 kidney transplant and 31 liver tarnsplant patients were analyzed. In both transplants, 60 ADRs to cyclosporine were reported including (number of cases), hypertension (19) and nephrotoxicity (6). In addition, 46 ADRs to tacrolimus were registered as hypomagnesemia (25), hypertension (7) and nephrotoxicity (5). A total of 95% and 96% of the adverse events to cyclosporine and tacrolimus, respectively, were defined as probable or definitive. Lastly, 70% and 98% of the events to cyclosporine and tacrolimus respectively, have been moderately severe or severe. Conclusions: This is the first study in Latin America that developed an intensive qualitative and quantitative analysis of the ADRs to calcineruin inhibitors in pediatric kidney and liver transplant patients. Spontaneous reporting should be motivated as well as monitoring ADRs should continue in the medium and long term for improving patient’s quality of life.