Benign prostatic hyperplasia (BPH) and associated lower urinary tract symptoms (LUTS) are highly prevalent in older men and represent a substantial challenge to public health. Increasing epidemiologic evidence suggests that diabetes and associated hyperglycemia and insulin resistance significantly increase the risks of BPH and LUTS. Plausible pathophysiologic mechanisms to explain these associations include increased sympathetic tone, stimulation of prostate growth by insulin and related trophic factors, alterations in sex steroid hormone expression, and induction of systemic inflammation and oxidative stress. This article presents a comprehensive update of the current understanding of clinical and epidemiologic research on diabetes and BPH/LUTS, describes hypothesized pathophysiologic mechanisms linking these conditions, and recommends future directions for research.