The safety characteristics of recent commercial lithium ion cells are examined in relation to their use for cellular phones. These are prismatic cells with an aluminum cell housing (can) and a 500–600 mA h capacity. They have one of two types of 4-V class cathodes, lithium cobalt oxide (LiCoO2) or lithium manganese oxide (LiMn2O4). This report provides results of the safety tests that we performed on lithium ion cells and outlines our views regarding their safety.