- Neurogenic Disorders (spinal cord and brain injuries, nerve disorders such as Parkinson's disease, Alzheimer's disease, multiple sclerosis, and stroke.)
- Hormonal Disorders (pituitary gland tumor; low level of the hormone testosterone).
- Arterial Disorders (peripheral vascular disease, hypertension; reduced blood flow to the penis).
- Cavernosal Disorders (Peyronie's disease.)
- Nonphysical causes: Mental disorders (clinical depression, schizophrenia, substance abuse, panic disorder, generalized anxiety disorder, personality disorders or traits.), psychological problems, negative feelings.
- Surgery (radiation therapy, surgery of the colon, prostate, bladder, or rectum may damage the nerves and blood vessels involved in erection. Prostate and bladder cancer surgery often require removing tissue and nerves surrounding a tumor, which increases the risk for impotence.)
- Aging.
- Lifestyle: alcohol and drugs, obesity, cigarette smoking.
- Other disorders.

A few causes of impotence may be iatrogenic (medically caused). Various antihypertensives (medications intended to control high blood pressure) and some drugs that modify central nervous system response may inhibit erection by denying blood supply or by altering nerve activity.

Surgical intervention for a number of different conditions may remove anatomical structures necessary to erection, damage nerves, or impair blood supply. Complete removal of the prostate gland or external beam radiotherapy of the gland are common causes of impotence; both are treatments for advanced prostate cancer. Some studies have shown that male circumcision may result in an increased risk of impotence, while others have found no such effect, and another found the opposite.

Excessive alcohol use has long been recognised as one cause of impotence, leading to the euphemism "brewer's droop," or "whiskey dick;" Shakespeare made light of this phenomenon in Macbeth.

A study in 2002 found that ED can also be associated with bicycling. The number of hours on a bike and/or the pressure on the penis from the saddle of an upright bicycle is directly related to erectile dysfunction.