BACKGROUND: Patients with diabetes have been found to have a preference for insulin pens over a vial and syringe since these devices offer improvements in compliance, freedom, and flexibility. OBJECTIVE: This study assessed the usability, specific pen features, and patient preference for 4 prefilled, disposable, insulin pens: Solostar, Humulin/Humalog pen (Lilly pen), FlexPen, and a fourth, prototype pen, Pen X, in patients with type 1 or 2 diabetes. In 1-hour interviews, patients carried out simulated use (preparing the pens, setting a dose, and injecting into a receptacle, not the body) under observation, and answered qualitative and quantitative questions. Patients were supplied with the relevant user manual. The usability (ability and time taken to carry out handling tasks) and preference (based on 14 key pen features and overall preference) of each pen were assessed without blinding for pen make/manufacturer. During the interviews, the patients prepared each pen and performed injections into a receptacle. Comparisons were made between the pens at every step. Subgroup analyses of the usability exercises were carried out based on age (11-15 years; >/=60 years), previous pen experience, and disability (visual and dexterity). RESULTS: In total, 510 diabetes patients (65% type 2 diabetes; 51% female; mean age, 43 years [range, 11-82 years]) from 4 countries (United States, Germany, France, and Japan) completed the study. Overall, a greater proportion of patients correctly prepared the pen and performed an injection into a receptacle with Solostar versus all comparator pens (P < 0.05). Similar findings were observed in the usability subgroup analyses based on age, previous pen experience, and visual/dexterity disabilities. A significantly (P < 0.05) higher proportion of patients expressed overall preference for Solostar (53%) versus FlexPen (31%) or Lilly pen (15%). CONCLUSION: Of the 4 pens compared, both the Solostar pen and FlexPen were found to have high patient usability, and the new Solostar pen was found to have high patient preference in these patients with diabetes.