The visual function and degree of retinopathy was assessed, over a three-year period, in a cohort study of twenty-eight diabetics, in whom glycaemic control was improved by intensive monitoring and supervision of conventional therapies. With the exception of visual acuity and some tests of visual field sensitivity, there was no significant change in visual functions or retinopathy; with improved control of blood glucose, these two visual functions showed a small initial deterioration and subsequently returned towards starting values. Six subjects required laser photocoagulation for progressive peripheral neovascularisation (including two subjects with peripheral new vessels), the six having a significantly longer duration of diabetes, slightly worse measures of extra-foveal retinal functions and a significantly greater reduction in haemoglobin A1 concentration during the first six months of the study. In this study, the improvement of blood glucose control by intensive supervision of conventional therapy did not appear to be associated with the significant acute deterioration of visual function or retinopathy that has been reported with the strict diabetic control by multiple daily insulin injections or continuous subcutaneous insulin infusion.