• Change From Baseline to Endpoint in the International Index of Erectile Function (IIEF)- Erectile Function Domain Score (Sum of IIEF Questions 1-5 and 15) [ Time Frame: Baseline and 12 weeks ] [ Designated as safety issue: No ]
• Improvement in the Sexual Quality of Life in the Subject and His Study Partner as Measured by the Sexual Quality of Life (SQoL) Domain of the Sexual Life Quality Questionnaire (SLQQ) [ Time Frame: Baseline and 12 weeks ] [ Designated as safety issue: No ]
• Change From Baseline to Endpoint in the Percent of "Yes" Responses to Sexual Encounter Profile (SEP) Diary Questions 2 (SEP2) and 3 (SEP3). [ Time Frame: Baseline and 12 weeks ] [ Designated as safety issue: No ]

• To evaluate the effect of tadalafil on sexual quality of life
• To evaluate the effect of tadalafil on Erectile Dysfunction

• Change From Baseline to Week 12 Endpoint in the International Index of Erectile Function - Intercourse Satisfaction Domain - Subject Response [ Time Frame: Baseline and 12 weeks ] [ Designated as safety issue: No ]
• Change From Baseline to 12 Week Endpoint in Overall Satisfaction Domain of the International Index of Erectile Function (IIEF-OS) - Subject Response [ Time Frame: Baseline and 12 weeks ] [ Designated as safety issue: No ]
• Sexual Life Quality Questionnaire (SLQQ) Treatment Satisfaction Domain [ Time Frame: 12 weeks ] [ Designated as safety issue: No ]
• Change From Baseline to 12 Week Endpoint in Percent of "Yes" Responses to Sexual Encounter Profile (SEP) Questions 4 and 5 - Subject Response [ Time Frame: Baseline and 12 weeks ] [ Designated as safety issue: No ]
• Change From Baseline to 12 Week Endpoint in Percent of "Yes" Responses to Partner-Sexual Encounter Profile (SEP) Question 3 - Partner Response [ Time Frame: Baseline and 12 weeks ] [ Designated as safety issue: No ]
• Change From Baseline to 12 Week Endpoint in the Satisfaction Domain of the Female Sexual Function Index (FSFI) - Partner Response [ Time Frame: Baseline and 12 weeks ] [ Designated as safety issue: No ]
• Percent of Subjects With "Yes" Responses to Global Assessment Questionnaire (GAQ) - Subject Response [ Time Frame: 12 weeks ] [ Designated as safety issue: No ]
• Percent of Partners With "Yes" Responses to Global Assessment Questionnaire (GAQ) - Partner Response [ Time Frame: 12 weeks ] [ Designated as safety issue: No ]
• Change From Baseline to 12 Week Endpoint in Percent of "Yes" Responses to Partner-Sexual Encounter Profile (SEP) Questions 1 and 2 - Partner Response [ Time Frame: Baseline and 12 weeks ] [ Designated as safety issue: No ]
• Change From Baseline to 12 Week Endpoint in the Self-Esteem and Relationship (SEAR) Questionnaire [ Time Frame: Baseline and 12 weeks ] [ Designated as safety issue: No ]
• Change From Baseline to 12 Week Endpoint in the Self-Esteem and Relationship (SEAR) Questionnaire - Confidence Domain Subscales [ Time Frame: Baseline and 12 weeks ] [ Designated as safety issue: No ]

• To evaluate tadalafil 5 mg once daily compared with placebo in improving intercourse satisfaction in the subject and his female study partner
• To evaluate tadalafil 5 mg once daily compared with placebo in improving sexual satisfaction in the subject and his female study partner
• To evaluate tadalafil 5 mg once daily compared with placebo in improving treatment satisfaction in the subject and his female study partner

To determine if tadalafil 5 mg daily compared to placebo when given for 12 weeks improves getting and maintaining an erection in men with erectile dysfunction and if there are improvements in the sexual quality of life of the man and his female study partner

• Drug: tadalafil
• Drug: Placebo

• Placebo Comparator: Placebo
• Active Comparator: 5 mg tadalafil

Inclusion Criteria:

Male

• History of erectile dysfunction (ED) for at least 3 months duration
• Anticipate having the same female partner willing to participate throughout the study
• At least 18 years of age at Visit 1 and agree to make at least 4 sexual attempts during the early phase of the study
• Adequate partner sexual function as determined by a Female Sexual Function Index
• Willing to record responses to efficacy questionnaires, sexual quality of life questionnaires and other instruments used in the study

Exclusion Criteria:

• May not participate in the study if you have taken tadalafil previously.
• History of cardiac conditions including angina requiring treatment with nitrates, heart disease of coronary conditions including myocardial infarction, bypass surgery, angioplasty or stent placement for specified time before starting the study.
• Have sexual partner not willing to complete the scales.
• Use of nitrates.