Disorders caused by single mtDNA deletions are quite rare in the general population. To understand the molecular mechanism by which they come about and try to correlate the type of deletion with the phenotype of the patients, a very large cohort of affected individuals needs to be studied. We have performed a meta-analysis of 313 deletions found in CPEO, KSS and PS patients. Our results indicate that the percentage and location of the deletion show differences between these syndromes. Thus, the moment when the deletion is produced probably not only determines the affected tissues and the phenotype, but also the percentage and location of the deletion.