The aim of this longitudinal study was to assess possible changes in sexual inhibition and excitation (measured using the Sexual Inhibition and Sexual Excitation Scales (SIS/SES)) in men being treated with PDE5 inhibitors (PDE5I) for ED. Established PDE5I users diagnosed with psychogenic ED completed the SES/SIS questionnaire at recruitment and 3 months later. On the basis of International Index of Erectile Function scores at recruitment, subjects were divided into two groups - mildly affected (M) and mild-to-moderately affected (MM). SES scores were significantly lower, and SIS1 scores were significantly higher in Group MM at recruitment and at 3 months (P<0.001). In Group M, SES scores increased (P<0.005) and SIS1 (P<0.001) and SIS2 (P=0.01) scores decreased over the 3 months of the study. In Group MM, ongoing decreases in SES and increases in SIS1 scores were observed (P<0.001). The results of multiple linear regression showed that SIS/SES variables were of little value in predicting erectile function (EF) at recruitment, or changes in EF during the study period. The results for Group M showed that men whose EF scores increased were more likely to experience increased SIS2 and decreased SES scores.