Over the past decade, it has been observed that anaemia is not just a symptom but also a risk factor for heart failure, first all-cause hospitalisation, cognitive impairment and mortality. Existing research recognised the prevalence to be increasing with age, while a high rate of anaemia could not be allocated to a specific cause. In previous studies on unexplained anaemia, low testosterone has been found to play a potential role in the pathogenesis of anaemia in the elderly. The present study sets out with the aim of quantifying anaemia in the elderly in Germany and of assessing whether low testosterone is a risk factor for developing anaemia. For this cause, a population-based cohort study with men and women between the ages 45 and 85 years was used. The criteria for the definition and classification of anaemia were aligned to the World Health Organisation guidelines and to previous research.The prevalence of anaemia was found to be rising with age to over 10% in the oldest age group which identified elderly men and women as a group vulnerable to anaemia. Furthermore, the prevalence of older men was higher than of older women. Among all anaemia cases, 46.95% remained unexplained. Anaemic people had on average lower iron stores, were older and had worse kidney function than non-anaemic people. Testosterone levels were lower in anaemic than in non-anaemic people and while the testosterone in men declined with age, it rose with age in women. Independent of age and body mass index, low testosterone was found to be a risk factor for developing anaemia and unexplained anaemia in the future for men and women. Moreover, the relationship between testosterone and anaemia was stronger for women than for men. The findings suggest that low testosterone might be a potential cause or co-cause in the development of unexplained anaemia, a disease that particularly rises with older age and has shown severe consequences on cognition, overall health and mortality.