['This study examined whether individuals with insomnia and objective short sleep duration <6h, a subgroup with greater risks of adverse health outcomes, differ in their response to cognitive behavioral therapy for insomnia (CBT-I) when compared to individuals with insomnia and normal sleep duration >6h.', 'Secondary analyses of a randomized, clinical trial with 60 adults participants (n=31 women) from a single academic medical center. Outpatient treatment lasted 8 weeks, with a final follow-up conducted at 6 months. Mixed-effects models controlling for age, sex, CBT-I treatment group assignment, and treatment provider examined sleep parameters gathered via actigraphy, sleep diaries, and an Insomnia Symptom Questionnaire (ISQ) across the treatment and follow-up period.', 'Six months post-CBT-I treatment, individuals with insomnia and normal sleep duration >6h fared significantly better on clinical improvement milestones than did those with insomnia and short sleep duration <6h. Specifically, individuals with insomnia and normal sleep duration had significantly higher insomnia remission [ISQ<36.5; X2(1, N=60) =44.72, P<.0001], more normative sleep efficiency on actigraphy [SE>80%; X2(1, N=60) =21, P<.0001], normal level of MWASO <31 minutes [X2(1, N=60) =37.85, P<.0001], and a >50% decline in MWASO [X2(1, N=60) =60, P<.0001] compared to individuals with insomnia and short sleep duration. Additionally, those with insomnia and normal sleep duration had more success decreasing their TWT at the 6-month follow-up compared to those with insomnia and short sleep duration [X2(2, N=60) =44.1, P<.0001]. Receiver operating characteristic curve analysis found that using a 6-h cutoff with actigraphy provided a 95.7% sensitivity and 91.9% specificity for determining insomnia remission, with the area under the curve = 0.986.'] Do insomnia Patients with Objective Short Sleep Duration have a Blunted Response to Cognitive Behavioral Therapy for Insomnia?