ABSTRACT Introduction The Erection Hardness Score (EHS), a validated single-item patient-reported outcome (PRO), may provide a simple method to capture erectile dysfunction (ED) symptoms and to monitor treatment outcome. Aim To map the relationship between the EHS, which was used as the anchor, and other validated PROs: International Index of Erectile Function (IIEF), Quality of Erection Questionnaire (QEQ), Sexual Experience Questionnaire (SEX-Q), and Self-Esteem and Relationship questionnaire (SEAR). Methods Data were from a trial of flexible-dose sildenafil (50 or 100 mg) in 209 men with ED. Main Outcome Measures A mixed-effects repeated-measures model with EHS as a categorical explanatory variable and each of the other PROs, as a separate dependent variable, was applied to analyze the longitudinal data from randomization to the end of the 10-week, double-blind, placebo-controlled phase and the 6-week open-label phase. EHS data, which were generated at each sexual encounter (event), were averaged per patient over the same recall period that preceded administration of the other PRO questionnaires. Results Scores on all domains of the IIEF and SEX-Q, as well as the SEAR total score and SEAR Sexual Relationship domain, discriminated on all EHS categories. The QEQ total score discriminated on all EHS categories except EHS 1 and EHS 2. Although the model did not impose any functional relationship between PRO score and EHS, an approximately linear relationship existed between the EHS and all other PROs, which was especially pronounced for those PROs that were more directly related to erectile quality or function. Conclusions The relationship between discrete EHS categories and PRO scores demonstrates the close correspondence of erectile hardness with erectile function (IIEF), erection quality (QEQ), overall sexual experience (SEX-Q), and ED-related psychosocial factors (SEAR) in men with ED. Cappelleri JC, Bushmakin AG, Symonds T, and Schnetzler G. S coring c orrespondence in o utcomes r elated to e rectile dysfunction treatment on a 4-point scale (SCORE-4). J Sex Med 2009;6:809–819.