Diphallia is a genetic condition present at birth in which a person has two penises. This rare condition was first written about in a report by the Swiss doctor Johannes Jacob Wecker when he encountered a cadaver exhibiting the condition in 1609.

Diphallia only affects about 1 out of every 5–6 million baby boys. In fact, only about 100 cases have been recorded over the past 400+ years since it was first medically recognized.

The condition of having two penises is alone not dangerous. However, diphallia is associated with many other conditions that do cause medical problems. People with diphallia often experience other congenital defects, including digestive and urinary tract problems.

When a baby boy is born with diphallia, doctors may note abnormalities in his penis, scrotum, or testicles. Below are the two most common ways that this condition manifests, according to The Human Phenotype Ontology. Between 80 and 99 percent of people with diphallia exhibit one or both of these manifestations:

  • penis divided into two parts (called penile duplication)
  • scrotum divided into two parts (called cleft scrotum)

Additionally, this condition manifests in several other, less common ways. Between 30 and 79 percent of people with diphallia exhibit one or all of these manifestations:

  • anal atresia
  • distal urethral duplication
  • ectopic scrotum (abnormal scrotum position)

Below are some of the less common manifestations of diphallia. Only 5–29 percent of boys with diphallia experience these:

  • abnormal rotation of the kidneys
  • abnormal sperm production
  • abnormality of the pubic bone
  • atrial septal defect
  • bladder exstrophy, a surgical procedure to repair a birth defect in which the kidneys grow outside the body
  • cryptorchidism, or undescended testicle
  • double ureter
  • epispadias, or abnormal placement of the opening of the penis
  • extra kidney
  • horseshoe kidney
  • inguinal hernia

Diphallia is a congenital genetic condition, which means it’s caused by hereditary factors that are out of one’s control. There is no single known factor that plays into a baby boy developing with this condition, nor are there preventative measures that pregnant mothers can take. Doctors and scientists simply don’t have enough cases available to make definitive statements.

Any person who exhibits signs and symptoms of diphallia should see their doctor as soon as possible so that they can be examined for common related conditions. Even if a person’s diphallus doesn’t bother them in daily life, it’s important to check the health of the rest of their body, especially their gastrointestinal system.

In developed countries, doctors will usually detect this condition in an infant at birth. However, the severity of the condition is part of a diagnosis. Severity is determined by the level of penile or scrotal separation that each person exhibits. One way of doing this is using the three-level Scheneider classification: glans diphallia, bifid diphallia, and complete diphallia.

Surgical intervention is the only line of treatment. Surgery usually involves cutting off the extra phallus and its urethra. Doctors aim to take the least obtrusive route possible when helping patients, so diphallus surgery may not always be required.

People born with diphallia can live to a normal age and enjoy rich, fulfilling lives. Diphallia is not terminal, and it can be fixed. It’s almost always noted at birth, and a plan for treatment can be started in infancy. Patients with this condition should talk to their doctor about the best way for them to move forward if they wish to treat their condition.