Obstructive sleep apnea (OSA) is a common condition among middle-aged men and is often associated with reduced testosterone (T) levels. OSA can contribute to fatigue and sexual dysfunction in men. There is suggestion that T supplementation alters ventilatory responses, possibly through effects on central chemoreceptors. Traditionally, it has been recommended that T replacement therapy (TRT) be avoided in the presence of untreated severe sleep apnea. With OSA treatment, however, TRT may not only improve hypogonadism, but may also alleviate erectile/sexual dysfunction.