Background: Phlebitis is a major adverse event. It has a high prevalence, ranging from 25.8% to 55.6%, which makes it an epidemiologically relevant phenomenon. Objective: To identify the prevalence of peripheral intravenous catheter-related phlebitis in patients admitted to a hospital unit in the North region of Portugal in May 2017, as well as to analyze its associated risk factors. Methodology: Prospective cohort study. Data were collected in May 2017 at a hospital unit in the North region of Portugal using the Portuguese version of the Phlebitis Scale, as well as patients' medical records for the collection of sociodemographic and clinical data. The sample was composed of 58 patients. Results: The participants had a mean age of 64 years, 53.4% of them were women, and the mean dwell time of the peripheral venous catheter (PVC) was 3.25 days. The prevalence of phlebitis was 36.7%, with a predominance of Grade 1 phlebitis (63%). Conclusion:The occurrence of phlebitis was associated with the PVC dwell time. Further studies and interventions should be conducted to raise nurses' awareness of the importance of assessing the type and severity of phlebitis.