Twenty clinicians, basic scientists and a patient representative from 10 countries gathered in Naarden, The Netherlands, to discuss the severe disorders of mtDNA maintenance, collectively termed mtDNA depletion syndromes (MDS) [1,2]. At present the majority of cases of MDS can be divided into two categories; patients have defects in either (1) nucleotide metabolism or (2) replication factors (see Table 1). Both types of defect are likely to cause problems and potentially stalling of the replication fork. The intramitochondrial nucleotide pool is both critically important in these disorders [3] and can be manipulated pharmacologically. Of all mitochondrial disorders they thus have the most immediate potential for developing treatments. The aims of the workshop were to discuss the pathogenesis of these disorders, underlying nucleoid biology, nucleotide pools and possible therapies.