Continuous subcutaneous insulin infusion (CSII) treatment may improve long-term glycemic outcomes and enhance quality of life compared with a multiple daily injection (MDI) insulin regimen for people with type 1 diabetes. As the number of people treated with CSII via a tubeless insulin pump is increasing, there is growing interest in the long-term glycemic outcomes of this treatment option across diverse populations. This multicenter, retrospective study evaluated glycemic control in 156 adults with type 1 diabetes initiating tubeless insulin pump therapy following transition from either MDI or CSII with a tubed insulin pump. In this study, use of the tubeless insulin pump over 12 months was associated with significant improvement in A1C in adults with type 1 diabetes, most notably in those with an A1C ≥9.0% and those previously treated with MDI.