Contrast sensitivity was studied in diabetic adolescents and young adults with and without retinopathy in order to evaluate their central vision, to analyze the relationship of metabolic control to the presence and severity of retinopathy, and to re-evaluate the response to this test after a significant improvement in metabolic control. Twenty adolescent and young adult diabetics without retinopathy and 40 diabetics with retinopathy of varying degree were enrolled in the study; 20 healthy age and sex-matched subjects served as controls. Contrast sensitivity was assessed with a CSV-1000 contrast testing instrument, testing for four spatial frequencies, 3, 6, 12 and 18 cycles per degree (cpd). Diabetics with no retinopathy showed a weak but significant difference at 18 cpd compared with controls (P = 0.04), while diabetics with background retinopathy showed a significant reduction of contrast sensitivity at 12 and 18 cpd when compared with controls (P < 0.001). In patients with preproliferative/proliferative retinopathy a highly significant reduction of contrast sensitivity at all frequencies was found compared with controls. Furthermore, these patients had a significantly lower mean contrast sensitivity than patients without retinopathy. The patients were re-evaluated after a significant amelioration of metabolic control. An improvement in contrast sensitivity was found in diabetics without retinopathy and with background retinopathy, while there was no change observed in diabetics with severe retinopathy. These results show that diabetic adolescents and young adults with and without signs of retinopathy observed by fluorescein angiography have a reduced contrast sensitivity, which is more severe in patients with preproliferative/proliferative retinopathy. A significant amelioration of metabolic control is associated with an improvement of contrast sensitivity in all patients with the exception of those patients who had signs of preproliferative/proliferative retinopathy observed by fluorescein angiography. In summary, this longitudinal study provides the first evidence that reduced contrast sensitivity is reversible in diabetics with or without background retinopathy only.