Peripheral intravenous access (PIA) is a necessity in the treatment and monitoring of the majority of hospitalised patients. Patients with an increased body mass index (BMI) more often than normal-weight patients have a difficult PIA. Identifying veins with ultrasonography has proven helpful when facing a difficult intravenous (IV) access. We hypothesise that, with the help of ultrasonography (US), it is possible to identify at least one vein suitable for IV access in morbidly obese patients (BMI40 kg/m(2)).We included 55 morbidly obese patients with a BMI40 kg/m(2). We performed a detailed US of seven anatomic areas routinely used for PIA. We present a description of parameters that are relevant when attempting PIA.In our study group, all patients had a minimum of one peripheral vein that was suitable for peripheral venous access, including seven patients (12.7%) who did not have clinically detectable veins.With the aid of US it is possible to identify a minimum of one peripheral vein suitable for IV access in morbidly obese patients.none.not relevant.