When a drug has important benefits as well as serious risks a RMAP can valuably affect the risk-benefit balance; for the product natalizumab (Tysabri) this enabled the product to resume marketing after being halted when cases of a rare severe brain infection occurred. Insufficient information was available to confidently determine how to eliminate that risk, or even if such was possible. As the demonstrated benefits of natalizumab were of potentially great importance to patient’s care, the risk-benefit balance was difficult to judge. A decision was made to allow natalizumab to return to the market within the structure of a RMAP. The specific risks and uncertainties of this situation, and how the RMAP in this instance contributed to minimization, mitigation, and evaluation of the risk will be described, such that the RMAP became a key element in allowing resumption of marketing.