This paper aims to address the ethical issues regarding prenatal diagnosis and preimplantation genetic diagnosis (PGD) of mitochondrial disorders. Owing to the absence of effective treatment, the prevention of the transmission of mitochondrial disorders is considered to be of key importance. The characteristics of mtDNA, such as heteroplasmy and the genetic bottleneck, make it difficult to estimate recurrence risks correctly and to provide an accurate prognosis for many mtDNA mutations. A limited number of mtDNA mutations allow reliable predictions, though results in the 'grey zone' are problematic. Both prenatal diagnosis and PGD for mtDNA disorders are complicated by the interpretation of the test results. As a consequence, these applications confront both clinical practice and society at large with several ethical questions and issues for further debate, among which the acceptability of suboptimal genetic testing, the value and research use of embryos, the evaluation of late abortion, the ethics of PGD for disorders with an incomplete penetrance and variable expression, the possible transfer of embryos with residual health risks, the acceptability of risks and drawbacks of genetic reproductive technology in general, and the scope and limits of reproductive autonomy and professional responsibility.