Treatment of male hypogonadism by testosterone substitution has be monitored in terms of safety. This study relates to safety of a new long-acting preparation.

A reliable form of androgen substitution therapy regarding kinetics, tolerance and restoration of androgenicity is paramount in hypogonadal men. Intramuscular injection of the long-acting ester testosterone undecanoate (TU) offers a new modality.

The objective is to assess safety of TU regarding metabolic and pharmacogenetic confounders in hypogonadal men treated with this new formulation.

This is a longitudinal prospective one-arm open intervention and observation trial. A minimum of 5 individual assessments is a prerequisite. Investigated modulators of safety parameters entering regression models are: nadir and/or delta total testosterone concentrations, body mass index (BMI), and age.

The setting Andrological outpatient department.

Inclusion Criteria:

• Men presenting hypogonadism-related symptoms and desiring substitution therapy. Such symptoms are fatigue, loss of libido, depressiveness, change in body composition/weight, decreased physical performance, decrease in aggressive behaviour, disability to cope, decreased work performance, lack of androgenization. At least one of these symptoms has to be accompanied by low total testosterone levels (< 12 nmol / L).
• All patients have to give written informed consent for the use of their data for scientific evaluation as approved by the Ethics Committee of the Medical Faculty, University of Muenster, Germany and the State Medical Board.

Exclusion Criteria:

• Prostate Cancer
• Breast Cancer
• Desired Paternity