Sex and gender differences in psychopathology have been understudied, yet identifying and understanding variability by sex and gender is important for the development of comprehensive etiological models as well as effective assessment and treatment of psychopathology in all persons. In the current article, we discuss the importance of sex and gender in psychopathology research, review terminology used when examining these constructs, and present multiple explanations for differential prevalence rates. Next, we review articles from psychopathology journals and conclude that researchers more often include both males and females than they did two decades ago, but still do not consistently analyze by sex or gender. We also provide an update of male-to-female ratios as presented in the DSM-5 and conduct a systematic review of the literature for selected disorders. We conclude that the DSM-5 presentation of sex or gender ratios is not systematic. Finally, we provide suggestions for the next DSM task force, researchers, journal editors, and funding agencies. These recommendations focus on more consistently and systematically considering sex and gender in all aspects of psychopathology research. (PsycINFO Database Record (c) 2019 APA, all rights reserved).