PURPOSE: Nocturia is one of the most bothersome lower urinary tract symptoms (LUTS). The aim of the present study is to determine whether severe-nocturia have impact on the abnormal daytime sleepiness in men with LUTS/benign prostate hyperplasia (BPH). MATERIALS AND METHODS: Severe-nocturia was classified as twice or more per night. A total of 85 men met the criteria and constituted the study cohort. The patients had a detailed clinical evaluation, including a complete history, physical examination, urine analysis, urine culture, a digital rectal examination, serum prostate-specific antigen (PSA) level, prostate volume by transrectal ultrasonography, uroflowmetry and postvoid residual urine volume. LUTS and symptom-specific quality of life (QoL) were assessed using the IPSS. Patients were asked to complete an Epworth Sleepiness Scale questionnaire for daytime sleepiness. RESULTS: 43 patients had less than one, 42 patients had more than two episodes of nocturia. There was no significant difference of age, total prostate volume, PSA levels between patients with mild-nocturia and severe-nocturia. There was no significant difference of maximum flow rate (Qmax), voided volume and postvoid residual urine volume (PVR) between patients with mild-nocturia and severe-nocturia. There was significant decrease of total International Prostate Symptom Score (IPSS) scores and QoL index in patients with severe-nocturia compared in patients with mild-nocturia. The number of patients with abnormal daytime sleepiness in mild-nocturia and severe-nocturia were 4.7% (2/43), 16.7% (7/42), respectively (p<0.05). Regression coefficiency between percent of nocturia and total score of daytime sleepiness was significant (p<0.05) and regression coefficient (R) was 0.29. CONCLUSIONS: Our results indicate that severe-nocturia had impact on the abnormal daytime sleepiness in patients with LUTS.