The backbone of any field of science is quality data. In personality disorder (PD) science and the broader field of clinical psychology, researchers must consider whether participants were attentive to, understood, and responded honestly and with sufficient effort to self-report questionnaires. We review literature regarding the prevalence of invalid (i.e., careless, low effort, inattentive, or inaccurate) responding, its impact on analysis and interpretation, and available methods of detection. We also present the results of a systematic review of 251 empirical articles across three major journals to characterize the current state of questionable data detection in PD science both in absolute terms and as compared to practices in the larger field of clinical science. In response to the disconcertingly low prevalence rate of self-report validity checks (approximately 22% of PD studies), we conclude by providing practical recommendations for improving data validity in PD science at the points of study design, data analysis, and reporting of results. (PsycInfo Database Record (c) 2023 APA, all rights reserved).