BACKGROUND: Aesthetic physicians rely upon certain anecdotal beliefs regarding the safe practice of filler injections. These include a presumed safety advantage of bolus injection after a negative aspiration. OBJECTIVES: The article aims to review and summarize the published literature on inadvertent intravascular injection of hyaluronic acid and to investigate whether the technique of aspiration confers any safety to the practitioner and the patient. METHODS: Pertinent literature was analyzed and our understanding of the safety of negative and positive aspiration outlined. RESULTS: The available studies demonstrate that aspiration cannot be relied upon and should not be used as a safety measure. It is safer to adopt injection techniques that will avoid injecting an intravascular volume with embolic potential than use an unreliable test to permit a risky injection. CONCLUSIONS: To prevent intravascular injection, understanding "injection anatomy" and injection plane and techniques such as slow, low-pressure injection are important safety measures. Assurance of safety when delivering a bolus after negative aspiration, does not appear to be borne out by the available literature. If there is any doubt about the sensitivity or reliability of a negative aspiration, then there is no role for its use. Achieving a positive aspiration would just defer the risk to the next injection location where a negative aspiration would then be relied upon.