The introduction of insulin pens has helped improve adherence in Type 1 or 2 diabetes, and reduce inaccurate dosing, fear of injection, and social embarrassment associated with vial and syringe. This report presents the published evidence base for the accuracy, patient preference and economic evaluation of one prefilled pen, FlexPen (Novo Nordisk A/S, Bagsvaerd, Denmark) and discusses recent changes to the design of this pen. Primary research publications that included the study of FlexPen were identified from various sources. Several studies have shown that FlexPen delivers high, medium and low doses of insulin significantly more accurately than vial and syringe, SoloStar (sanofi-aventis, Paris, France) or OptiClik (sanofi-aventis, Paris, France). Patients have also found FlexPen easier to use than vial and syringe. A Next Generation FlexPen has been developed, which maintains the demonstrated accuracy of FlexPen and is accompanied by a reduced injection force for simpler and more comfortable use, and clear colour scheme for insulin type to avoid medication errors.