There is still a debate as to whether or not glucose variability contributes to diabetes complication risk. There is much in vitro laboratory evidence that glycaemic instability gives rise to increased production of reactive oxygen species and has a detrimental effect on endothelial dysfunction. While some in vivo studies have also shown similar findings in patients with or without diabetes, others have been unable to confirm any association. Furthermore, clinical studies which have sought to translate this possible risk into an increased likelihood of developing micro- or macrovascular complications have so far not demonstrated an effect. However, few of these trials were specifically designed to establish any influence of glucose fluctuations. This issue is now one of the largest remaining unanswered questions in diabetes. While this article focuses on the data which do not support a role for glucose variability in the development of complications, it also highlights the need for further studies to be performed which will definitively resolve the matter.