Malposition of a catheter is found in approximately 7% of cases after central venous catheterisation. This may result in haemorrhage, venous thrombosis and functional impairment, depending on the injury to the vessel wall. Uncomplicated catheterisation, easy aspiration of blood and monitoring of catheterisation do not guarantee correct placement of the catheter. In our rare case series, we share our experience of four cases of malposition into the left internal mammary vein (LIMV) that we experienced in a three-year period. The thinness and fragility of the vessel wall, particularly, increases the probability of complications in malposition into the LIMV. Administration of a catheter through the right jugular vein is associated with the lowest incidence of malposition. Performing the procedure under the guidance of ultrasonography (USG) and confirmation of the catheter position after puncture using one of the USG techniques will minimise the probability of malposition. In addition, a lung X-ray should immediately be taken, and venography and fluoroscopy should be considered in the presence of suspicion.