Abstract: Background information. The yeast mitochondrial F 1F o-ATP synthase is a large complex of 600 kDa that uses the proton electrochemical gradient generated by the respiratory chain to catalyze ATP synthesis from ADP and Pi. For a large range of organisms, it has been shown that mitochondrial ATP synthase adopts oligomeric structures. Moreover, several studies have suggested that a link exists between ATP synthase and mitochondrial morphology. Results and discussion. In order to understand the link between ATP synthase oligomerization and mitochondrial morphology, more information is needed on the supramolecular organization of this enzyme within the inner mitochondrial membrane. We have conducted an electron microscopy study on wild type yeast mitochondria at different levels of organization from spheroplast to isolated ATP synthase complex. Using electron tomography, freeze fracture, negative staining and image processing we show that cristae form a network of lamellae, on which ATP synthase dimers assemble in linear and regular arrays of oligomers. Conclusions. Our results shed new light on the supramolecular organization of the F 1F o-ATP synthase and its potential role in mitochondrial morphology.