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.
Sometimes doctors will recommend gender reassignment, so the child is brought up as a girl.
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.