Androgen deprivation therapy (ADT), used increasingly in the treatment of localized prostate cancer, is associated with substantial long-term adverse consequences, including incident diabetes. While previous studies have suggested that ADT negatively influences glycemic control in existing diabetes, its association with diabetes complications has not been investigated. In this study, we examined the association between ADT use and diabetes complications in prostate cancer patients. A retrospective cohort study was conducted among men with newly diagnosed localized prostate cancer between 1995 and 2008, enrolled in three integrated health care systems. Men had radical prostatectomy or radiotherapy (curative intent therapy), existing type II diabetes mellitus (T2DM), and were followed through December 2010 (n = 5,336). Cox proportional hazards models were used to examine associations between ADT use and diabetes complications (any complication), and individual complications (diabetic neuropathy, diabetic retinopathy, diabetic amputation or diabetic cataract) after prostate cancer diagnosis. ADT use was associated with an increased risk of any diabetes complication after prostate cancer diagnosis (adjusted hazard ratio, AHR, 1.12, 95% CI 1.03-1.23) as well as an increased risk of each individual complication compared to non-use. ADT use in men with T2DM, who received curative intent therapy for prostate cancer, was associated with an increased risk of diabetes complications. These findings support those of previous studies, which showed that ADT worsened diabetes control. Additional, larger studies are required to confirm these findings and to potentially inform the development of a risk-benefit assessment for men with existing T2DM, before initiating ADT.