• Decrease in height
• Enlarged breasts (gynecomastia)
• Infertility
• Lack of muscle mass
• Lack of sex drive (libido)
• Loss of armpit and pubic hair
• Slow development or absence of secondary male sex characteristics (growth and distribution of hair, scrotal enlargement, penis enlargement, voice changes)

Men may also notice they do not need to shave as frequently.

A physical examination may reveal:

• Genitals that do not clearly look either male or female (usually noted in infancy)
• Abnormally small testicle
• Tumor or mass (group of cells) on or near the testicle

Further testing may show decreased bone mineral density and fractures. Blood tests may reveal low levels of testosterone and high levels of prolactin, FSH, and LH.

Testicular failure and low testosterone levels may be difficult to diagnose in older men because testosterone levels normally fall with age. The level of testosterone at which replacement therapy would be likely to improve symptoms and other outcomes is unpredictable and variable.