Purpose Benign prostatic hyperplasia is a common disease in men that until recently was considered a single disease with varying symptoms. Our recent analysis has revealed that a molecular marker, JM-27, is able to distinguish at the tissue level between highly symptomatic individuals and those with histological disease. The goal of these studies was to determine if a serum based assay to detect JM-27 could distinguish men with different forms of benign prostatic hyperplasia. Materials and Methods A serum based enzyme-linked immunosorbent assay was developed using a novel anti-JM-27 monoclonal antibody. The assay was sensitive, detecting JM-27 at the low ng/ml level within the serum. A quantitative measurement of serum JM-27 levels was performed in 68 patients. The patients consisted of 3 groups of 29 patients with asymptomatic benign prostatic hyperplasia (American Urological Association symptom score of 15 or less), 39 with symptomatic benign prostatic hyperplasia (American Urological Association symptom score 16 to 32) and 17 with confirmed prostate cancer. The assay cutoff was determined after a pilot run of samples and applied prospectively. Results Using the determined cutoff, serum levels of JM-27 can distinguish between symptomatic and asymptomatic patient sets. The sensitivity and specificity of the assay are 90% and 77%, respectively. The presence of prostate cancer in these men does not appear to alter the marker levels. Conclusions The present study is believed to represent the first characterization of a serum based marker for severe benign prostatic hyperplasia.