Hypogonadism can begin during fetal development, before puberty or during adulthood. Signs and symptoms depend on when the condition develops.

Fetal development
If the body doesn't produce enough testosterone during fetal development, the result may be impaired growth of the external sex organs. Depending on when hypogonadism develops and how much testosterone is present, a child who is genetically male may be born with:

Female genitals
Ambiguous genitals - genitals that are neither clearly male nor clearly female
Underdeveloped male genitals

Puberty
Male hypogonadism may delay puberty or cause incomplete or lack of normal development. It can cause:
Decreased development of muscle mass
Lack of deepening of the voice
Impaired growth of body hair
Impaired growth of the penis and testicles
Excessive growth of the arms and legs in relation to the trunk of the body
Development of breast tissue (gynecomastia)

Adulthood
In adult males, hypogonadism may alter certain masculine physical characteristics and impair normal reproductive function. Signs and symptoms may include:
Erectile dysfunction
Infertility
Decrease in beard and body hair growth
Decrease in muscle mass
Development of breast tissue (gynecomastia)
Loss of bone mass (osteoporosis)

Hypogonadism can also cause mental and emotional changes. As testosterone decreases, some men may experience symptoms similar to those of menopause in women. These may include:
Fatigue
Decreased sex drive
Difficulty concentrating
Hot flashes