Diphallia, penile duplication (PD), diphallic terata, or diphallasparatus, is an extremely rare developmental abnormality in which a male is born with two penises. The first reported case was by Johannes Jacob Wecker in 1609. Its occurrence is 1 in 5.5 million boys in the United States.When diphallia is present, it is usually accompanied by renal, vertebral, hindgut, anorectal or other congenital anomalies. There is also a higher risk of spina bifida. Infants born with PD and its related conditions have a higher death rate from various infections associated with their more complex renal or colorectal systems. It is thought diphallia occurs in the fetus between the 23rd and 25th days of gestation when an injury, chemical stress, or malfunctioning homeobox genes hamper proper function of the caudal cell mass of the fetal mesoderm as the urogenital sinus separates from the genital tubercle and rectum to form the penis. The first case was reported by Wecker in Bologna, Italy, in 1609, and since then, about one hundred cases have been reported. This condition has existed in humans since ancient times. The two external genitalia may vary in size and shape, either lying beside each other in a sagittal plane or one above the other in a frontal plane.According to Schneider classification in 1928, double penis is classified into three groups: (a) glans diphallia, (b) bifid diphallia and (c) complete diphallia or double penis.
The meatus may be normal at tip of glans, hypospadiac, or epispadiac; the scrotum may be normal or bifid. True diphallia is more likely accompanied with associated anomalies and malformations compared with bifid phallus. Infants born with diphallia have higher death rate due to infections associated with anomalies. Complete true diphallia with associated anomalies
A two-day-old male newborn, associated with complex genitourinary and ano-rectal malformation. He had imperforated anus, hypospadias, bifid scrotum, meatuses on both glandes, two bladders and two colons, and had normal testes, kidneys and ureters. Partial true diphallia or pseudodiphallia, without associated anomalies
Partial true diphallia corresponds to pseudodiphallia. Pseudodiphallia is formed from erectile tissue only, undifferentiated and non-functional. It is independent of the normal penis  and can be removed surgically without problem. This rare case was reported, based on the age of the 83-year-old man when diphallia was only detected then when he was hospitalised, and also because of the absence of other anatomical malformations. The small, immature and nonfunctional penis protruded on one side of the large, normal penis. The secondary penis had glans but without urinary meatus. Complete bifid diphallia with associated anomalies
A 12-year-old boy, associated with bifid scrotum, epispadia and pubic symphysis diastasis. He had two separate penises, similar in size and shape, each penis had an epispadia urethral meatus. He had bifid scrotum, one testicle on each side of the scrotum. A bowel loop-like structure was over the pubis region. This structure had no communication with any other structures. He had a single normal bladder and ureter.