Background <p>Fear of pain during insulin injection, using pen injectors, still represents a barrier to diabetes treatment. The development of smaller and thinner needles has improved comfort during the injection, but the influence of other needle geometry features, has been less thoroughly assessed. The aim of this review, is to evaluate the role that pen needle geometry plays in determining patient experience during insulin injection.</p> Methods <p>A literature search was conducted in PubMed and Scopus to identify the publications assessing the effect of needle geometry and quality on insertion force and pain, experienced by the patient during injection. 22 studies were included in this review. All studies included, at minimum, an evaluation of the perceived injection pain, using a Visual Analogue Scale (VAS).</p> Results <p>The clinical evidence demonstrated that in addition to the pain reduction experienced with increasing needle gauge, other geometrical features such as shorter needle length, thinner wall design, improved tip geometry and coating with lubricant, are associated with reduced injection pain and improved patient experience. Furthermore, it was indicated that the needle features shown to help reduce the experienced pain, would not negatively affect the frequency and intensity of injection related site reactions or needle-related failures, such as breakage and bending.</p> Conclusions <p>Pen needle geometry affects the insulin injection experience of diabetic patients. Increased needle gauge, shorter length, improved tip design and mechanical characteristics of the needle are all associated with a perceived reduction of the pain during insulin injection and an overall improved patient experience.</p>