Certain subgroups of youth are at high risk for depression and elevated depressive symptoms, and experience limited access to quality mental health care. Examples are socioeconomically disadvantaged, racial/ethnic minority, and sexual minority youth. Research shows that there are efficacious interventions to prevent youth depression and depressive symptoms. These preventive interventions have the potential to play a key role in addressing these mental health disparities by reducing youth risk factors and enhancing protective factors. However, there are comparatively few preventive interventions directed specifically to these vulnerable subgroups, and sample sizes of diverse subgroups in general prevention trials are often too low to assess whether preventive interventions work equally well for vulnerable youth compared to other youth. In this paper, we describe the importance and need for "scientific equity," or equality and fairness in the amount of scientific knowledge produced to understand the potential solutions to such health disparities. We highlight possible strategies for promoting scientific equity, including the following: increasing the number of prevention research participants from vulnerable subgroups, conducting more data synthesis analyses and implementation science research, disseminating preventive interventions that are efficacious for vulnerable youth, and increasing the diversity of the prevention science research workforce. These strategies can increase the availability of research evidence to determine the degree to which preventive interventions can help address mental health disparities. Although this paper utilizes the prevention of youth depression as an illustrative case example, the concepts are applicable to other health outcomes for which there are disparities, such as substance use and obesity.