INTRODUCTION Erectile dysfunction (ED) is distressing and can affect a couple's relationship. AIM To investigate partner awareness of ED, relationship problems, and the effects of tadalafil treatment over 12 months. METHODS The Determinants of Continued Use of Tadalafil study is a prospective 12-month European observational study in patients with ED initiating or changing treatment to on-demand tadalafil. A total of 1,900 patients were enrolled in eight countries. Assessments were made on predefined treatment outcomes in a routine clinical setting. MAIN OUTCOME MEASURES At baseline, 1, 6, and 12 months, patients were asked about relationship problems (unspecified), partner awareness and support of consultation, and partner sexual problems. Data were analyzed for patients continuing tadalafil at 12 months. RESULTS At baseline, 96% of patients had a partner, 80% of partners supported an ED consult, and 73% were aware of the consultation. Relationship problems were reported by 17% of patients at baseline. At 12 months, 84% of patients were still taking tadalafil. Of these, 19% reported relationship problems at baseline. After 12 months of treatment with tadalafil, 4% of patients still reported perceived problems. Factors associated with no relationship problems at 12 months were: at baseline, no previous ED treatment, partner in poor health; and at 12 months a lower ED severity. If the partner was felt to have a sexual problem at 12 months, relationship improvement was less likely. Further, 3% of patients developed relationship problems during treatment. Factors associated with developing a relationship problem were: a history of pelvic surgery at baseline, a different partner at 12 months than at baseline, and a partner with a sexual problem at 12 months. CONCLUSIONS Improvement of ED with tadalafil was associated with reduced relationship problems, suggesting that problems were associated with ED and resolved with treatment.