Objectives: Electroconvulsive therapy (ECT) administration rises in frequency with age, with older depressed adults often showing clinical features predictive of good response. Recent reviews suggest that older people experience few if any long-term cognitive adverse effects after contemporary ECT, despite their increased vulnerability to these. However, the broader clinical validity of research findings is not assured as most studies of ECT-related cognitive effects do not discuss cognitive test nonparticipants. This study examines whether cognitive test participants and nonparticipants are comparable. Methods: We recently completed a study of cognition in depressed patients 65 years and older treated with ECT. Only 35 of eligible patients completed neuropsychological testing at 2 time points, the remainder either refusing or unable to consent. To examine whether exclusion of most eligible patients from cognitive testing might have affected the clinical applicability of findings, we compared demographic and clinical characteristics of patients who participated with those who did not based on a subset of patients from our original study. Results: The 2 patient groups differed in several respects. Most notably, nonparticipants were significantly more likely to be involuntary patients; to refuse food and fluids; and to require treatment with a bitemporal or mixed electrode placement. Conclusions: Our findings suggest cognitive test nonparticipants to be more severely psychiatrically unwell than test participants. As their exclusion might bias results and confound understanding of this important ECT-related topic, special mention of participation rates and comparison of participants and nonparticipants is recommended to establish the clinical relevance of future study findings.