In this clinical column, we discuss the ambiguous distinction between genetic research and clinical genetics, particularly for Mendelian diseases with high recurrence risk, high morbidity and/or mortality and the possible amelioration of such diseases by screening or treatment. We use arrhythmogenic right ventricular cardiomyopathy as an example of a lethal Mendelian disorder, which prompted the discussion contained in this column. Working with such diseases may mean that genetic researchers have some responsibility for both immediate research subjects and their extended families, as they obtain molecular genetic information. For some diseases, therefore, a willingness to accept genetic research results should be an inclusion criterion, and it may be considered unethical for research ethics boards to approve genetic studies unless measures to ensure clinical follow-up have been established. We recommend managing the tensions between genetic research and clinical practice by using disease-based genetic registers, organized within a clinical genetic service.