Incidents or deviations in the administration of medication are a major public health problem due to its consequences in hospital morbidity and costs. Materials and methods: descriptive study of a series of retrospective cases in a hematology service in a university hospital in Colombia (Hospital de San José de Bogotá). The search and collection of data in the clinical histories was performed by intrahospital cycles of chemotherapy from January to December 2011. Incidents or errors in the administration of the medication were evaluated. Results: 508 incidents were found: incorrect recording of the time (22.4% of the cycles), lack of previous information session (14.7%), without informed consent (13.3%), absence of a checklist ( 12.9%), incorrect signature of the medical protocol (8.66%), incorrect signature of the nursing protocol (10.0%), lack of correlation between medical and nursing protocol (5.31%), incorrect registration of the medication (4.52%), incorrect dose (2.36%), incorrect registration of the route (1.37%) and absence of the report of adverse effect (0.19%). Conclusions: the identification of the most frequent incidents will allow to establish strategies and recommendations to avoid them and to make a safer practice of administration of chemotherapy.