Surgeons are perfecting a way to build up the size of very small penises, enabling proper urination, and a full sex life.
It is estimated that about one in 200 men is born with what is known as a micro-penis.
Whereas the average size of the human penis is around 12.5cm (5 inches), a micro-penis spans less than 7cm.
University College London surgeons will present their work to the European Society for Sexual Medicine.
A micro-penis can develop from inadequate levels of the male sex hormone testosterone during the second and third trimesters of pregnancy, or from an inability to respond to testosterone in the normal way.
The technique has been carried out on nine men. Click below to see images.
WARNING: These images show male genitals in close-up.
In the past doctors have recommended gender reassignment, so the child was brought up as a girl, but this is a practice which has ceased in recent years.
However, there are a number of treatments available.
The UCL team has been refining a technique called phalloplasty, or penile enlargement.
This involves cutting a flap of skin from the patient's forearm and shaping it into a penis four or five inches long.
To maintain erogenous sensation, the original penis is incorporated into the surface of the transplanted skin.
Patients receive a urethra to enable them to urinate, and an inflatable penile prosthesis to allow an erection to engage in sexual intercourse.
UCL surgeons performed the operation on nine men aged 19 to 43 with a range of medical backgrounds, including three hermaphrodites and two men who had problems with androgen (the group of hormones which includes testosterone), one of whom became deficient in androgen after chemotherapy.
Following surgery, all patients were found to be satisfied with the cosmetic appearance of their penis, with four patients able to urinate standing up and four able to have regular sexual intercourse.
However, in several cases multiple complications arose, such as an infection or a shift in the prosthesis position, with subsequent revision operations needed.
Dr David Ralph, of UCL's Institute of Urology, said: "This operation can change the life of young men, improving their self-esteem and quality of life and allowing many of them to have sexual intercourse, sometimes for the first time in their life.
"However, patients should be aware of the high risk of complications from this procedure."