ABSTRACT OBJECTIVE To report on the out-of-pocket expenses incurred by insulin- treated patients to manage blood glucose levels. METHODS This retrospective study in insulin-using adults with type 1 or type 2 diabetes was conducted between July 7 and December 12, 2003, in 4 Canadian centres, using a patient self-administered questionnaire and medical charts. The questionnaire collected data regarding duration of diabetes; duration of insulin therapy; type of diabetes; source of payment for insulin, oral antihyperglycemic agents and test strips (i.e. insurance company [with % coverage], government, self); average cost per month to treat hypoglycemia; frequency of self-monitoring of blood glucose and insulin injections; and frequency of diabetes-related visits to healthcare professionals. RESULTS All 335 patients enrolled completed the study; 202 (60.3%) had type 1 diabetes and 133 (39.7%) had type 2 diabetes; 29 patients (8.6%; 27 type 1 and 2 type 2 diabetes patients) used pump therapy. The mean out-of-pocket cost per person for all patients was $2.21 daily or $807 annually ($891 for type 1 and $679 for type 2 diabetes). Insulin pump users had higher annual average costs than non-pump users ($1309 vs. $797). At 39.2% of total expenses, glucose monitoring test strips accounted for the greatest cost, followed by management of hypoglycemia (26.1%), insulin (15.8%), syringes and needles (11.7%), and insulin pump and supplies (3.9%). CONCLUSIONS This study provides direct data confirming that the costs of managing blood glucose are significant for people with diabetes treated with insulin. Ensuring that people with diabetes do not receive compromised care because of financial constraints is a challenge that will require a coordinated and thoughtful response from healthcare providers, all levels of government, the insurance industry, formulary listing bodies and patient advocacy groups.