ALTHOUGH there have been experimental studies of the structure of the C60 molecule in the gas phase1 and the solid state at low temperature2, so far only indirect experimental details of the structure of the C70 molecule have been available3. The ellipsoidal structure for C70, the subject of recent theoretical work4,5, should provide a useful test of current understanding of carbon–carbon bonding, in that a single molecule contains several distinct types of bond in various relationships to pentagonal and hexagonal rings. Conventional crystallographic techniques are not suitable for studying C70 at room temperature because of poor crystallinity and orientational disorder in solid samples. Here we present the results of a study in which the molecular structure of C70 was deduced from electron diffraction using a simulated-annealing method. The 'rugby' ball structure is confirmed, with a slight pinching of the waist, and the bond lengths are found to follow a simple pattern determined by their relationship to the five and six-membered rings.