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Electric vehicles are sometimes marketed unambiguously as low-carbon technologies; however, they often contain less ‘clean’ ingredients, such as rare earth permanent magnets. In fact, high-performance permanent magnets in electric vehicles often use neodymium. Alternatively, more costly samarium-cobalt magnets can be used. In this paper, life cycle assessment is used to compare the primary production routes of both neodymium-iron-boron and samarium-cobalt magnets in terms of environmental impact. For primary production of samarium-cobalt magnets, this is the first detailed life cycle inventory published to date. In addition, we provide an updated life cycle assessment of neodymium-iron-boron, expanded with recent literature and some primary industry data. We conclude that production of samarium-cobalt is not preferable in terms of environmental impact, from a cradle-to-gate perspective. A sensitivity analysis and uncertainty analysis show that while there are uncertain parameters in both studies, the uncertainty range tends to be slightly higher for samarium-cobalt.