Stressful or traumatic events have been shown to impair cognitive functioning on laboratory-based tasks due to stress-related intrusive thoughts and avoidance. However, research on the effects of stress on everyday cognitive functioning has been lacking. A sample of 909 undergraduates completed measures of perceived stress, PTSD symptoms, and everyday cognitive failures. The results revealed that both perceived stress and PTSD symptoms uniquely predicted cognitive failures, even after controlling for a number of potentially confounding variables. Additionally, there was a significant interaction. Participants with low scores on both measures of stress reported the fewest occurrences of everyday cognitive failures. In contrast, participants with elevated scores on either measure of stress reported higher levels of cognitive failures. These results suggest that there are unique negative effects of perceived stress and PTSD symptoms on everyday cognitive functioning and sharpen our understanding of the relationship between stress and cognition.