Objective Researchers have increasingly examined whether participants who have experienced a traumatic event should be considered vulnerable research populations. Studies have typically asked participants in trauma‐focused research whether they were upset by the study or perceived any benefit from it. The current study extends such research by measuring mood and exploring potential moderators of the impact of study participation. Method Participants were 107 women who experienced a traumatic or stressful event and completed an event‐focused research protocol. Negative affect was measured, using the Positive and Negative Affect Schedule, at the time of the study and 1 week later. Results Participants reported significantly lower levels of negative affect in the week after the study than before it. Decreases in negative affect were greatest for those with highest levels of depression at the time of interview. Conclusions Participation in a trauma‐ or stressful‐event‐focused study is not harmful and may even be beneficial, especially among depressed participants.