Health technology assessment is frequently credited with making difficult resource allocation decisions in health care fairer, more rational and more transparent. In Germany, a constitutional ‘right to health’ allows patients to challenge decisions by sickness funds to withhold reimbursement of treatment excluded from public funding because of insufficient evidence of effectiveness. The ability to litigate was qualified by the Constitutional Court in its 2005 ‘Nikolaus decision’ that sets out criteria to be applied to these cases. Treatment must be made available if (1) the condition is life-threatening, (2) no alternative treatment is available and (3) there is an indication that the treatment could benefit the patient. This paper examines how courts struggled to apply these criteria based on an analysis of cases of patients who sought treatment for cancer between 2005 and 2015, and explores the implications of applying a constitutional ‘right to health’ to treatment decisions.