Clinical practice guideline from the Endocrine Society regarding testosterone therapy in men with hypogonadism. It updates a previous 2010 guideline and was developed by a task force using an evidence-based approach. The guideline provides recommendations for diagnosing hypogonadism, including specific tests to use, and outlines the treatment of hypogonadism with testosterone, discussing various formulations and their pharmacokinetics. Importantly, it also addresses adverse events associated with testosterone therapy, such as erythrocytosis and potential cardiovascular and prostate risks, and provides guidance on monitoring patients receiving treatment, including specific follow-up schedules for testosterone, hematocrit, and prostate health. The document includes a commissioned systematic review summarizing the efficacy and adverse events of testosterone replacement therapy in hypogonadal men based on randomized, placebo-controlled trials.