This FOA solicits R01 projects that aim to evaluate the safety of testosterone administration in older men by assessing the relationship of testosterone administration to adverse outcomes in clinical practice. Applicants are encouraged to submit applications to conduct analyses of databases from health care systems or epidemiologic studies that contain information on diagnoses, therapies, and testosterone levels. Additional information on safety of testosterone administration is needed because, although several small short-term clinical trials have been conducted in older men, these studies do not provide adequate information to assess the safety of testosterone as used in clinical practice. This information is important for clinicians and their older patients in decisions regarding starting or continuing testosterone therapy. Moreover, adequate information on safety is lacking in regard to many important adverse outcomes, particularly in regard to long-term testosterone use.