Inclusion Criteria:

1. Patients with ED over 3 months (specify using IIEF score)
2. Age >= 18 years.
3. Stable sexual relationship
4. With low or low normal serum testosterone level (either total or bioavailable testosterone) TT <= 4 ng/ml and/or BT <= 1 ng/ml
5. Aging Male Symptom scale with total score starting at 37 points (must not replace TT < 4 ng/ml)
6. Eligible subjects who previously took the oral androgen or PDE5 inhibitor must have discontinued their use for 1 month

Exclusion Criteria:

1. Contraindication to treatment with Testosterone according to the SPC
2. Hypersensitivity to the active substances or any of the excipients of Nebido
3. Diagnosed or suspected carcinoma of the prostate or the male breast cancer
4. Past or present liver tumors
5. Acute or chronic hepatic diseases
6. Severe cardiac, hepatic or renal insufficiency
7. History of penile implant or significant penile deformity
8. Diagnosed sleep apnea
9. Polycythemia (Hematocrit >50%)
10. Prolactin >25 ng/ml
11. Organic hypothalamic-pituitary pathology
12. Any unstable medical, psychiatric or drug/alcohol abuse disorder
13. Prostate specific antigen (PSA)>= 4 ng/ml
14. Severe symptomatic benign prostatic hyperplasia (IPSS) sum score >=20)
15. Diabetes mellitus which is uncontrolled (HbAlc level >10%)
16. Epilepsy not adequately controlled by treatment
17. Patients requiring fertility treatment
18. Hypertension which is not adequately controlled on therapy
19. Clinically significant chronic hematological disease which may lead to priapism such as sickle cell anemia, multiple myeloma or leukemia
20. Hypersensitivity to PDE-5 inhibitors

21. Concomitant Medication:

    • Nitrites or Nitric oxide donors
    • Anti-androgens
    • anti-coagulants, with the exception of anti-platelet agents
    • Any of potent inhibitors of cytochrome P-450 3A4:such as HIV protease inhibitors (Ritonavir or Indinavir); Anti-mycotic agent (Itraconazole and Ketoconazole)-topical application allowed; or Erythromycin.