A reusable insulin pen (HumaPen(R) Ergo) was tested for patient acceptability and safety in two multinational studies involving a total of 230 patients with either type 1 (27%) or type 2 (73%) diabetes. Prior to the studies, all patients used other insulin injection pen models. During the 5-7-week studies, the acceptability of HumaPen Ergo was assessed with a questionnaire which was issued to all patients. The HumaPen Ergo was considered easy/very easy with respect to learning to use (97%), reading dose numbers (95%) and correcting dose mistakes (97%), and 62% considered it easy/very easy to hold during use. HumaPen Ergo features considered easier/much easier compared to the previously used model of pen were ease of correcting dose (Study 1/Study 2: 89%/93%), ease of reading the dose number (77%/61%) and ease of changing cartridge (54%/68%), At the end of the studies the majority of patients (60%/69%) said that they would continue to use HumaPen Ergo and would recommend it to other patients, even though they had expressed satisfaction with the pen that they had used previously. Health-care professionals evaluated HumaPen Ergo according to the same criteria as the patients and said that they would recommend the HumaPen Ergo owing to ease of dialling back without wasting insulin (80%) and reading dose numbers (74%). The HumaPen Ergo was well accepted by both patients and health-care professionals and provides an important tool to combat the trauma and inconvenience associated with insulin self-injection.