OBJECTIVE: Increase in insulin therapy prescribed to diabetes patients has led to a demand for simple delivery devices that can be used for effective, self-injection. Selecting the most appropriate insulin delivery device for a given patient is likely to improve patient compliance and promote accurate dosing. Perceived usability and patient preference of the two prefilled insulin analog pen devices (FlexPen and Humalog Pen) were compared. METHODS: In a randomized, crossover study, 58 subjects (29 male, 29 female, average age 58 ± 16 years) who had not previously used insulin pen devices were randomized to test either FlexPen or Humalog Pen for 2 days. The subjects were then switched to alternate device for 2 days. Device assessments were carried out at the end of each 2-day test period. Following instructions, participants made simulated injections into a sponge on the abdomen to determine the usability of each insulin device. All subjects were tested for manual function and vision prior to commencing the study. RESULTS: FlexPen was rated significantly better than Humalog Pen for each of the usability questions: number legibility (p <0.001), ease of dose setting (p <0.001), ease of pressing the release button (p <0.001), stability during injection (p <0.001), simplicity (p <0.001), confirmation of injection (p <0.001), and appearance (p <0.01). No significant differences were observed between the two devices in measures of grip and portability. Overall, 83% subjects preferred FlexPen; 17% had no preference and no subjects preferred Humalog Pen. FlexPen was also rated as superior to Humalog Pen when subgroups of age, manual function and vision were examined (p <0.01 for each subgroup comparison of overall score for each pen). CONCLUSIONS: The perceived usability advantages of FlexPen were probably due to its scaled analogue dial (which shows completion of injection) and larger dial numbers. These results demonstrate that FlexPen achieved patient preference with a wide range of patients, including those with impaired vision and manual dexterity.