Background: The increasing prevalence of obesity, in particular in young patients, represents a growing clinical and health-care cost problem. Young adulthood obesity strongly increases the risk of type 2 diabetes (T2DM), hypertension, myocardial infarction, stroke or venous thromboembolism. Young obese T2DM men have a high prevalence of low testosterone concentrations indicating eugonadotropic hypogonadism. An existing but undetected testosterone defi ciency will substantially hamper weight loss or render it impossible. In such cases, returning the testosterone level to normal range is therefore the necessary precondition to fi ght obesity and thus the related comorbidities. Case presentation: A 20-year-old man with grade III obesity complained of fatigue, dry mouth, and erectile dysfunction (ED). Medical examination revealed uncontrolled T2DM, pronounced dyslipidemia, severe vitamin D defi ciency, and a remarkably low testosterone level. Medication with metformin and vitamin D was initiated and testosterone therapy (TTh) was started. Under TTh, the patient continuously lost weight, and his blood sugar and lipid profi le progressively normalized. Finally, a complete remission of T2DM was reached and all baseline complaints including ED were fully gone. Even after TTh was stopped, all respective values remained in the normal range. Conclusions: We conclude that TTh worked as a necessary stimulus along with standard therapy for consequential facilitation of weight reduction and associated recovery of the body's own production of testosterone in particular in terms of a complete remission of T2DM.