ABSTRACT Objective To review and summarize the human and veterinary literature pertaining to the diagnosis, treatment, and prevention of phlebitis. Etiology Phlebitis can occur in any patient with a vascular catheter, but the focus of this review is on its occurrence in association with peripheral venous catheters (PVCs). The three main categories of phlebitis are infectious, mechanical, and chemical; catheter‐, patient‐, or drug‐related factors may increase the risk. The most devastating injuries likely result from the extravasation of chemotherapeutics and drugs with certain properties (e.g., vasoactive, acidic or alkaline, hyperosmolar or hypo‐osmolar). Diagnosis Phlebitis is diagnosed based on clinical signs including erythema, swelling, edema, pain, and fever. In people, several grading scales exist to assess for the presence and progression or resolution of phlebitis, but no specific diagnostic or grading schemes exist for veterinary patients. Therapy Mild cases of phlebitis likely resolve after removal of the PVC; however, higher grades of phlebitis require more aggressive treatment. Nonpharmacologic therapies are instituted initially, and treatment is escalated to topical, local injectable, and parenteral therapies as indicated. There are several antidotes indicated after the extravasation of certain drugs, particularly chemotherapeutics. Nonpharmacologic phytotherapeutics have also been studied as ancillary therapies in people. Prognosis Phlebitis and extravasation injury are associated with morbidity and mortality in human and veterinary patients; however, the definitive prognosis for affected veterinary patients is unknown. It is advisable to implement prevention strategies. When considering prognosis, early identification and treatment of vascular injury are likely of greatest importance.