Crystalline SnO2 thin films have been investigated as possible negative electrodes for lithium-ion batteries. The films have been cycled electrochemically vs. lithium and shown reversible capacity as high as 500 mAh/g over more than 100 cycles. The substantial irreversibility during the first cycle can be explained by the formation of metallic tin and amorphous lithium oxide. This last phase probably plays an important role in allowing the thin-film electrode to contract and expand during the cycling process.