Testosterone deficiencies are identified and treated by the Urology Division of Premier Medical Group. Testosterone is a male hormone produced by the testicles. It is responsible for the proper development of male sexual characteristics as well as bone growth, muscle mass and sexual function. Production of testosterone naturally decreases with age, but it can also result from damage to the hypothalamus, pituitary gland, the testicles or systemic diseases. Testosterone deficiency is also known as hypogonadism, and depending on age, could result in problems with muscle and bone development, underdeveloped genitalia and reduced virility.