Observers with brain injury and control participants performed a vigilance task during which they received periodic whiffs of unscented air or air scented with peppermint. Under both fragrance conditions, controls reduced the frequency of commissive errors (false alarms) over the course of the vigil, an adaptive strategy given the low probability of signals employed (0.04). The false alarm rate of observers with brain injury increased precipitously toward the end of the vigil in the unscented air condition. However, exposure to the scent of peppermint rendered the false alarm scores of observers with brain injury similar to that of controls, a result which is consistent with evidence that olfactory stimulation activates brain areas vital for planning and judgment.