Depletion of mitochondrial DNA (mtDNA) causes defects in respiratory activity and energy production. Recent studies have shown mitochondria to exist primarily as reticular networks, having tubular cristae. Using fluorescence microscopy and transmission electron microscopy, we have examined mitochondrial morphology and interior structure in wildtype and mtDNA-depleted rho0 human fibroblasts and 143B osteosarcoma cell lines. MtDNA depletion results in compromise of the mitochondrial continuum and causes a reduction in amount of cristal membranes, often prompting the remaining cristae to adopt a circular appearance in the mitochondrial interior. These changes emphasize the tight relationship between mitochondrial structure and function.