OBJECTIVES Normoglycaemia in people with diabetes results in improved outcome. Continuous glucose monitoring provides detailed diagnostic information used to optimise therapy. The objective of this study was to review randomised controlled trials (RCTs) of the only device available for blinded, professional use. METHODS Published studies using the MiniMed Continuous Glucose Monitoring System (CGMS, Medtronic Inc., Northridge, CA) were identified using appropriate search terms in a series of clinical databases including: Medline, Pubmed, Google Scholar and Scientific Web of Knowledge. Other measures were also taken such as searching the reference lists and review by recognised experts. RESULTS Seven randomised controlled trials were identified, five in children. Double-blinding was not possible. Although HbA1c was explicitly stated as the primary endpoint in four studies the studies were only adequately powered to detect large, between-group minimum differences (range 0.5 to 1.0% HbA1c). Only two studies included subjects with type-2 diabetes. Other endpoints included the frequency of hypoglycaemia and hyperglycaemia events. Within-group HbA1c decreases were observed in all but one study. The crude, weighted mean improvement in HbA1c across the studies using the device was 0.6% (range 0% to 0.8%). No studies recorded how the information was utilised to modify treatment, such as changes in dose titration or treatment regimen. CONCLUSIONS Devices such as the professional CGMS provide detailed diagnostic information. However, any consequent changes in care and outcome can only result from the appropriate application of this information. Although there was a notable improvement in glucose control (HbA1c), existing studies were largely underpowered and did not capture the resulting treatment changes that could lead to improved outcome.