Objective: This study aimed to identify the incidence rate of infiltration, phlebitis, and risk factors in chemotherapy patients. Methods: This observational prospective cohort study was conducted in the oncology and hema- tology clinics of a hospital in Turkey. Peripheral intravenous catheter insertion sites (n = 175) on 99 patients were monitored. Researchers monitored the peripheral intravenous catheter inser- tion sites for 5 days after nurses inserted them. The ethics committee approved the study. Results: The incidence of infiltration and phlebitis was, respectively, 9.7% and 17.5%. The incidence rate of infiltration was significantly higher, respectively, in the case of vesicants and the presence of neutropenia among patients over 52 years of age. It was determined that the risk of infiltra- tion in women was 0.21 times higher than in men. When the neutropenia value was put into the model alone, it was determined that the risk of infiltration increased 0.414 times in the case of neutropenia. Conclusion: The patient’s gender, the presence of neutropenia, and the chemotherapy drug type affect the incidence of infiltration. Regular follow-up of the catheter site will reduce the workload of the nurse by ensuring the continuation of patient care and treatment without interruption. It will also reduce the frequency of the catheterization procedure and prevent the difficulties it brings to the patient.