• Old Age
• Decreased Blood flow
• Diabetes
• High Blood Pressure (Hypertension)
• Pelvic Surgery (Prostate, Bladder, Rectal)
• Spinal Cord Injury, Multiple Sclerosis 
• Hormonal Problems
• Depression and Psychological Problems
• Cigarette Smoking, Excessive Use of Alcohol, Drug Abuse
• Medications
• Sickle Cell Anemia
• Peyronie's Disease
• Premature Ejaculation

Erection: An erection occurs when the soft spongy tissue in the shaft of a man's penis fills with blood, causing the penis to enlarge and stiffen. Spongy spaces along the length of the penis fill with blood in response to physical stimulation, psychological stimulation, or both. This process requires that the blood supply and the nerve connections to the penis are working properly.

Premature ejaculation: Premature ejaculation may affect a man for all of his adult life or only with specific partners. The traditional approach has been to treat premature ejaculation with psychological counseling, but new drugs are showing some promise with helping this disorder

Smoking and Impotence: Impotence is the inability to have or maintain an erection. This condition effects roughly 1 in 10 men between the ages of 21 and 75. Risk of impotence is increased to nearly 50% by smoking cigarettes for men in their 30s and 40s. Diabetes, high cholesterol and drugs used to treat high blood pressure also increase the chances impotence. During an erection, blood flows into the penile arteries causing the veins which drain the penis to become compressed, preventing blood from leaving the penis. This process is significantly impaired by smoking. Less blood flows into the penis if the route is blocked by fatty deposits in the arteries, caused by smoking.

Impotency and Cholesterol: In a totally unrelated development (unrelated to aging, that is), National Institute of Aging supported scientists from the University of South Carolina have found yet another compelling reason to avoid cholesterol. Men with lower blood cholesterol or higher amounts of the beneficial high-density lipoprotein (HDL) cholesterol may be less likely to develop erectile dysfunction or impotence. According to the researchers, atherosclerosis (hardening of the arteries), which may impede blood flow to and from the penis, is one primary cause of impotence. While a positive link between blood cholesterol and atherosclerosis, the association between cholesterol and impotence has only been suggested until now.

Diabetes And Impotence: Achieving and maintaining an erection is a complex action in which blood circulation, nerves and hormones all play a role. Psychological and emotional factors are also important.