OBJECTIVE Continuous subcutaneous insulin infusion (CSII) is an effective method of intensive therapy for patients with type 1 diabetes; however, most studies have not examined long-term glycemic control. We evaluated the long-term efficacy of CSII in a cohort of adult patients with type 1 diabetes. METHODS This was a retrospective observational study of 200 patients with type 1 diabetes who initiated CSII at a single outpatient clinic in Kingston, ON, Canada between January 1998 and December 2012. Data were collected from 3 months prior to and up to 15 years after initiation of CSII and included glycated hemoglobin (HbA1c) level and demographic factors potentially associated with glycemic control. RESULTS Mean age and duration of diabetes at CSII initiation were 35.4 years and 22.4 years, respectively. Mean duration of CSII at the time of analysis was 6 years. Mean HbA1c at initiation of CSII was 8.7% and decreased to a nadir of 7.5% 6 months post-initiation (SD = 1.0) (P < 0.001). This increased over time (range, 7.8-8.2%) but remained lower than the pre-CSII HbA1c (P < 0.001). Shorter duration of diabetes prior to CSII initiation, history of missed appointments, mental illness, and active smoking were predictors of higher HbA1c on CSII. Pre-CSII HbA1c predicted long-term HbA1c on CSII. CONCLUSIONS The data demonstrate that in a clinic setting, patients on CSII maintain lower HbA1c values over a 1-10-year period compared with pre-CSII values. Poor pre-CSII HbA1c, history of missed appointments, mental illness, and active smoking are predictors of those less likely to achieve an HbA1c target of ≤ 7.0%.