Objective Insomnia is frequently comorbid with other medical and psychological disorders. This secondary data analysis investigated whether an Internet‐delivered cognitive behavioral therapy for insomnia (CBT‐I) intervention could also reduce comorbid psychological and fatigue symptoms. Method Data from a pilot randomized controlled trial (RCT) testing the efficacy of Internet‐delivered CBT‐I relative to a waitlist control was used to examine changes in symptoms of depression, anxiety, mental health quality of life (QOL), and fatigue. Results Group by time interactions from repeated measures analyses revealed significant post intervention improvements in Internet participants (n = 22) relative to control participants (n = 22) on all psychological symptoms, mental health QOL, and fatigue. A small post hoc subsample of Internet participants with mild or moderate depression also showed large effect size changes in these constructs (depression, anxiety, mental health QOL, and fatigue). Conclusion Internet‐delivered CBT‐I appears to not only improve sleep but also reduce comorbid psychological and fatigue symptoms.