This observational study assessed metabolic control in young, active professionals with type 1 diabetes treated with continuous subcutaneous insulin infusion (CSII) with or without the use of a bolus calculator. Eighteen patients aged 19 - 51 years with diabetes duration of 6 - 22 years were included; eight patients used a bolus calculator and 10 did not. Metabolic control was assessed by glycosylated haemoglobin (Hb(A1c)) measurements and blood glucose profiles. A continuous glucose monitoring system (CGMS) was also used by three patients from each group. Mean Hb(A1c) and fasting blood glucose levels were not significantly different between the two groups, but mean post-prandial blood glucose was significantly lower in bolus calculator users than non-users. The CGMS showed more blood glucose levels within the target range in bolus calculator users than non-users, but statistical significance was not achieved. In conclusion, a bolus calculator may help to improve postprandial blood glucose levels in active professional type 1 diabetes patients treated with CSII, but does not have a major impact on Hb(A1c) levels.