Introduction: Midline catheters are widely used in clinical practice. Proper placement of midline catheter tip is usually assessed only by aspirating blood and flushing with normal saline without resistance. Purpose: To describe the ultrasound-guided tip location for midline catheters and its feasibility and to compare incidence of catheter-related venous thrombosis associated with or without ultrasound tip localization. Methods: The ultrasound-guided tip location is described step by step. Feasibility of the technique and incidence of catheter-related venous thrombosis were measured (study group) and compared with two historical groups: study group, 20-cm midline catheters inserted with ultrasound-guided tip location; group 1, 25-cm midline catheters inserted without ultrasound-guided tip location and group 2, 20-cm midline catheters inserted without ultrasound-guided tip location. Results: In the study group, ultrasound-guided tip location was easily feasible in 98.9% of patients. Incidence of catheter-related venous thrombosis was 2.42% in control group 1, 9% in control group 2 and 2.62% in the study group. Discussion: In the study group and control group 1, the tip was placed in the axillary vein, about 3 cm distal to the clavicle and in the subclavian vein. In control group 2, the tip was probably located at the transition between the axillary and the subclavian vein. It is possible that such position may have been associated with an increased incidence of catheter-related venous thrombosis. Conclusion: The ideal position of the tip of a midline catheter might be inside the axillary vein, about 3 cm distal to the axillary-subclavian transition or inside the subclavian vein. Ultrasound-guided tip location is safe, inexpensive, easy and potentially useful during midline catheters insertion.