To test the impact of nasal dilator strips (NDSs) on insomnia severity, sleep-disordered breathing (SDB) symptoms, sleep quality, and quality of life. Randomized, controlled trial of 4 weeks' duration. Community sample of nonobese, adults with a primary sleep complaint of chronic sleep-maintenance insomnia and mild to moderate SDB symptoms (treatment, n=42; control, n=38). Primary outcomes were four validated scales: Insomnia Severity Index (ISI), Pittsburgh Sleep Quality Index (PSQI), Functional Outcomes of Sleep Questionnaire (FOSQ), and Quality of Life Enjoyment and Satisfaction Questionnaire (QLESQ). Secondary outcomes were sleep indices, nonrestorative sleep ratings, and SDB symptoms, assessed retrospectively and prospectively. Both groups received nonspecific education about sleep disorders. Treatment group also received a brief SDB education and nasal strip instructions. At 4 weeks' follow-up, the treatment group demonstrated significant (p=.0001), large improvements in ISI and PSQI (mean Cohen's d=1.18) and significant (p<.02), medium-sized improvements in FOSQ and QLESQ (mean d=0.51) compared to small, nonsignificant changes in control group (Cohen's d range=0.36-0.09). Treatment group change scores among all four primary variables were significantly correlated (mean r=0.50, p=0.01). Secondary prospective and retrospective outcomes showed medium to large improvements in treatment compared to controls for sleep indices (mean d=0.52 vs 0.28), nonrestorative sleep ratings (mean d=0.69 vs 0.11), and sleep breathing symptoms (mean d=0.47 vs 0.09). Significance was obtained for prospective sleep indices (p=0.01), retrospective, and prospective nonrestorative sleep ratings (p=0.003, <0.05), and retrospective sleep breathing symptoms (p=0.03). SDB education and NDSs demonstrated therapeutic efficacy in a select sample of insomnia patients with SDB symptoms. Replication of results requires placebo controls and objectively confirmed SDB cases.