To investigate details of sexual function of erectile dysfunction in Japanese patients taking phosphodiesterase type 5 inhibitors. A Japanese version of the Psychological and Interpersonal Relationship Scales-Short Form was used to carry out a nationwide survey using the Internet. A total of 556 erectile dysfunction patients (age 30-70 years) who had been prescribed a phosphodiesterase type 5 inhibitor and had attempted sexual intercourse within the past 6 months were included in this survey. Scores were compared in relation to the phosphodiesterase type 5 inhibitors most frequently taken within the past 6 months. In the subdomains of self-confidence and spontaneity of the Psychological and Interpersonal Relationship Scales-Short Form, scores for vardenafil and tadalafil were significantly higher than those for sildenafil. In the subdomain of time concern of the Psychological and Interpersonal Relationship Scales-Short Form, the score for tadalafil was significantly lower than that for others. Our findings support the hypothesis that Japanese patients with erectile dysfunction have high sexual self-confidence, spontaneity and low time concerns when taking tadalafil. These characteristics of tadalafil could be associated with high patient satisfaction and high preference.