BACKGROUND: Aspiration prior to hyaluronic acid filler injection is often taught as a safety maneuver to minimize the risk of intravascular injection. Its validity in aesthetic practice is being increasingly challenged. One key assumption underpinning the validity of the aspiration test is that the needle tip does not move during the aspiration and subsequent injection of filler. OBJECTIVES: To visualize and measure in real-time needle tip movement during aspiration and injection of filler. Secondary objectives were to assess the impact of double-handed versus single-handed aspiration technique, and injector experience in maintaining stability of the syringe. METHODS: Under real-time ultrasound visualization, 3 injectors of different experience level injected hyaluronic acid filler into pork belly tissue utilizing both double-handed and single-handed aspiration techniques. Needle-tip movements were recorded and measured on ultrasound and video. RESULTS: The aspiration maneuvers is associated with retrograde movement of the needle tip in all cases ranging from 1.1mm to 5.3mm (mean 2.9mm), while injection leads to anterograde movement ranging from 0.6mm to 4.1mm (mean 1.9mm). Double-handed aspiration is associated with less needle tip movement compared with single-handed aspiration (p=0.037). Greater experience is also associated less movement of the needle-tip (p<0.0001). CONCLUSIONS: In all cases, the aspiration and injecting maneuver is associated with micro-movements of the needle tip, of a magnitude consistently significant relative to the typical size of facial vessels. While needle tip movement is but a single factor that limit the usefulness of the aspiration test, the results of this study suggest that it is not advisable to solely rely on aspiration as a method of preventing intravascular injection.