Abstract To determine the incidence of unused out-of-hospital intravenous line (IV) placements, we prospectively studied IV placement in emergency medical services (EMS) patients. Unused IV placement was defined as any patient having an EMS initiated IV that was not used for fluid bolus or medication administration in the field or in the emergency department (ED). Data were analyzed on placement and use of IV lines in the field and in the ED, transport time, years of paramedic practice, and paramedic student presence. Of 290 patients, 165 had an IV initiated (147) or attempted (18). Twenty-nine percent (84 of 290) of the patients received an unused EMS IV. One hundred twenty-five patients had no IV initiated by EMS. Seven subsequently had an IV started and used in the ED, for an undertreatment rate of 2.4% (7 of 290). The presence of a paramedic student increased the odds of an unused IV 1.4 (95% Cl, 1.1 to 2.0). IVs are frequently started and not used.