We investigated urine nerve growth factor (NGF) levels and erectile dysfunction in diabetic men <45 years of age. Urinary NGF levels were measured in 72 diabetic men and 20 control subjects without lower urinary tract symptoms or erectile dysfunction. Participants were evaluated using the International Prostate Symptom Score, quality of life index, Overactive Bladder Symptom Score (OABSS), the five-item version of the International Index of Erectile Function questionnaire (IIEF-5), the patient perception of bladder condition questionnaire, measurement of flow rate and post-void residual urine volume. The results showed that the diabetic men had significantly higher urinary normalized NGF/creatinine (Cr) levels compared to the healthy controls (0.48±1.2 vs 0.01±0.01, P=0.04). The increased urinary NGF/Cr levels correlated negatively with the IIEF-5 total score (P=0.03, coefficient=-0.26, -0.02 to -0.47). The 42 patients with urinary NGF/Cr levels <0.05 had higher IIEF-5 scores than the 30 patients with urinary NGF/Cr level ⩾0.05 (20.2±4.6 vs 16.9±6.7, P=0.03). We conclude that urinary NGF levels were associated with erectile dysfunction in the men with type 2 <45 years of age.