Objective To investigate the clinical and urodynamic features of patients with lower urinary tract symptoms/benign prostatic hyperplasia (LUTS/BPH) according to their prostate size. Materials and Methods We analyzed 2039 LUTS/BPH patients who underwent urodynamic study between October 2004 and August 2013. We divided the patients into three groups according to their prostate size: small (≤30 mL), moderately enlarged (31-80 mL), and large prostate (≥81 mL) groups. We compared the groups regarding age, International Prostatic Symptom Score, maximal flow rate (Qmax), postvoided residual (PVR), serum prostate-specific antigen, prostate volume measured by ultrasonography, and urodynamic findings. Results Patients with a small prostate had better urodynamic outcomes than those with larger prostates in overall population. Although the total prostate volume significantly correlated with the bladder outlet obstruction (BOO) index (r = 0.51), BOO patients with a small prostate had similar Qmax, higher PVR, and lower voiding efficiency, compared to those with larger prostates. Moreover, urodynamic parameters indicating bladder abnormalities, including low compliance and involuntary detrusor contraction positivity, were similar among the groups in BOO patients. A higher proportion of detrusor underactivity was also observed in the small prostate group in BOO patients. Finally, when adjusting for potential confounding variables, we identified serum prostate-specific antigen levels (odds ratio, 1.34) and Qmax (odds ratio, 0.77) as significant predictors for BOO in LUTS/BPH patients with a small prostate. Conclusion BOO patients with a small prostate showed higher PVR and poor voiding efficiency, as well as similar urodynamic bladder abnormalities, compared to those with moderately enlarged and large prostates.