The primary objective of the Registry of HYpogonadism in MEn (RHYME) is to establish and maintain a large, multi-national prospective registry of male patients who have been diagnosed with male hypogonadism (HG), also known as androgen deficiency or testosterone deficiency.

Inclusion Criteria:

1. Male patients aged 18 years and older.
2. Diagnosis of hypogonadism including Klinefelter's or late onset HG. Patients may have been diagnosed at any point in their lives. Documentation of the diagnosis of HG (including symptomatology and laboratory values including testosterone levels confirmed on two separate occasions) is required.
3. Written informed consent.

Exclusion Criteria:

1. Any previous treatment with testosterone therapy.
2. History of breast cancer, prostate cancer, or high-grade prostatic intraepithelial neoplasia.
3. Prior radical prostatectomy.
4. Life expectancy shorter than 24 months as judged by the Clinical Site investigator.
5. Current major psychiatric disorders or drug or alcohol abuse, which will likely affect participation or compliance in the Registry, in the opinion of the Clinical Site Investigator.
6. Gender dysphoria or sexual reassignment (e.g., transexualism).
7. Patients actively enrolled in any interventional clinical trial.
8. Planned relocation outside Clinical Site region within 24 months.

Hypogonadal men