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Micropenis: Symptoms, Causes and Treatments

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Micropenis is a medical term for a condition usually discovered in infants through a newborn examination. As the term suggests, micropenis refers to an abnormally small but normally structured penis. The condition is caused by hormonal or genetic abnormalities.

Important things to know about a micropenis:

  • Some men may believe they have a micropenis, but that’s likely not the case. It’s very rare.
  • A micropenis has a stretched penile length (SPL) of less than 2.5 standard deviation (SD) below the mean for the male’s age.
  • In men, an SPL of 3 2/3 inches or less indicates a micropenis. The average SPL for adult males is 5.25 inches.
  • Genetics (family history) may play a role in the condition.
  • There is no cure for micropenis but hormone therapy may be done for children to stimulate penile growth.

How common is micropenis?

Micropenis happens rarely. Estimates vary, but studies indicate 0.6 percent of men worldwide have the condition. In the years 1997-2000, 0.015 percent (1.5 in 10,000 births) of boys in the United States were born with micropenises.

What are the symptoms of micropenis?

The primary symptom of micropenis is a penis that measures less than 1.9 cm (0.75 inches) in length at infancy. The mean (average) stretched penile length for a newborn is 3.5 cm (1.4 inches).

Micropenis is diagnosed if the length is less than 2.5 standard deviation below the mean. In adult males micropenis is defined as a penis as 3 2/3 inches or less.

Micropenis may accompany other health problems due to hormonal disorders or congenital (present at birth) conditions, which can cause a variety of symptoms. Your child’s symptoms will depend on the cause of the micropenis.

What are the causes of micropenis?

Micropenis is usually caused by fetal testosterone deficiency which can be the result of a variety of conditions. The most common is hypogonadotropic hypogonadism.

Hypogonadotropic hypogonadism is a condition that occurs when the hypothalamus (the part of the brain that controls the autonomous nervous system and pituitary) does not secrete the hormones that stimulate the testicles to produce hormones (testosterone) necessary for normal maturation and reproductive function.

Micropenis may also be found with genetic syndromes that can cause other malformations. Or the condition may be idiopathic (have an unknown cause).

How is micropenis diagnosed?

Micropenis is diagnosed through a physical examination. Usually found in infancy or young childhood, micropenis is diagnosed through measurement of penile length.

Chances for treatment of micropenis are greater if it is diagnosed in infancy. The doctor can diagnose a true micropenis by fully stretching the penis and measuring with ruler, caliper or modified 10 ml disposable syringe. The number is compared to the normal size range of the boy’s age.

A diagnostic workup follows to determine what kind of treatment should be used to stimulate penis growth.

How is micropenis treated?

Testosterone treatment

Treatment of micropenis depends on the cause of the condition and each child is different. It’s important that treatment begin in infancy or very early childhood.

The first treatment is a short course of testosterone. This treatment tests the ability of the penis to respond to the growth hormone. Testosterone can be given with an injection or applied to the area as a gel or ointment. Studies show that penile growth is good with testosterone treatment in many infants, but whether the growth continues during puberty an adulthood is not known.

Other hormonal treatments may be tried if the testosterone treatment doesn’t add length to the penis.


Surgery for micropenis is only considered when medical treatments don’t work. Surgical reconstruction (phalloplasty) of the micropenis for younger children is complicated and risky but worth exploring. Surgery for young adults and adults is more common.

If you are a man considering surgery for your micropenis, make sure you clearly understand what the risks and benefits of the surgery are for your particular situation.

Primary care physicians, pediatric endocrinologists and when necessary surgeons need to keep parents aware of all options and potential outcomes.

What is the prognosis (outlook) for patients with micropenis?

With early treatment the prognosis for boys with micropenis due to hormone deficiency is good. They usually respond well to testosterone therapy, gain adequate penile length (though below average size) and are able to function normally as adults.

The outlook is not as positive for those boys with micropenises that are due to other disorders, such as androgen insensitivity, who can’t be helped with hormone treatment. In these cases, the penis remains small.

How do patients and their families cope with micropenis?

If early treatment is unsuccessful for micropenis, coping with the condition can be difficult for a boy and his family.

In all cases, psychological counseling and social services will probably be required to help the patient and his family emotionally.

Micropenis is a rare condition and what to do about the condition depends on many factors. Your doctors will help you along with your decisions as a parent or as a patient.

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