Objective: The objective of this study was to identify the incidence of infiltration and extravasation in newborns using peripheral venous catheter, and affecting factors. Method: This observational study examined catheters inserted into newborns who received inpatient care in the neonatal intensive care unit of a state hospital located in the west of Turkey. A total of 452 peripheral venous catheters inserted into 152 newborns were observed. The forms were completed by the researchers based on their observations at each shift. Results: The infiltration/extravasation occurred in 45.6% of peripheral venous catheters inserted into newborns; 19.7% were stage I and 11.7% were stage IV. A statistically significant relationship was found between the gestation week as well as the birth weight of newborns and the occurrence of infiltration/extravasation complication. In addition, there were statistically significant relationships between the administration of single or multiple antibiotics, total parenteral nutrition and the incidence of infiltration/extravasation complication. Conclusion: It is recommended to use an appropriate scale for the assessment of infiltration/extravasation as well as to implement measures for preventing the occurrence of infiltration/extravasation.