This study investigated the relationship among anxiety, depression, and sleep disturbances and the treatment of these three disorders through neurotherapy. Research suggests that these conditions commonly co-occur in the general population and that central nervous system (CNS) arousal may play a primary role in the development and maintenance of these disorders. Several recent studies suggested that neurotherapy, a biofeedback-based treatment for CNS dysregulation, might be an effective treatment for comorbid conditions, particularly the ones of interest here, depression, anxiety, and sleep disturbances. This investigation used a clinical case-series design to assess pre/post neurotherapy changes on objective measures of anxiety, depression, and sleep and to determine whether changes in anxiety and depression then predict improvements in sleep quality. Data for 23 participants (10 males) were obtained from files of adults (Mage = 40.22 years, SD = 16.20) who received at least 15 neurotherapy sessions (M = 47.83 sessions, SD = 22.23) the University of North Texas Neurotherapy Lab. Matched pair t-tests revealed that symptoms of sleep disturbance, depression, and anxiety showed significant improvements following neurotherapy. Neurotherapy treatment effect sizes generally ranged from moderate to large (d = .414 - .849). Multiple regression analysis found that changes in self-reported anxiety symptoms, but not depressive symptoms, predicted observed improvements in sleep quality (adjusted R2 = .26). Last, the implications and limitations were discussed in relation to neurotherapy practice and the associated research.