Efforts to improve inclusion in research have included mandating the recruitment of ethnic minorities and women into NIH funded studies. However, little research has been completed on who attends such interventions. This is particularly worrisome in populations for which attendance to interventions can have dire consequences. HIV is a public health concern for pregnant women in substance using communities, as pregnant women are much less likely to use condoms during intercourse to prevent HIV. Group modular HIV prevention interventions have long been the standard for HIV prevention. However, little attention in research on HIV prevention interventions RCTs has been focused on attendance to these interventions. This study examined predictors of intervention and control group attendance in a randomized controlled trial comparing a 5-session Safer Sex Skill Building (SSB) intervention to a 1-session HIV education control group in a sample of pregnant women at risk for prenatal substance use. This study identified psychosocial and mental health variables associated with both 1 session control group and 5-session SSB intervention attendance as well as endeavored to identify the number of sessions necessary to attend to achieve an adequate dose in treatment. Findings include younger age and marital status as being predictive of participation in the one session HE control group and having a trade, skill, or profession as being predictive of participation in the five session SSB intervention group. Further research is needed to understand what factors may impact five-session SSB group attendance.