Insomnia and obstructive sleep apnea (OSA) are common sleep disorders and frequently coexist (COMISA). Arousals from sleep may be a common link explaining the frequent comorbidity of both disorders. Respiratory arousal threshold (AT) is a physiologic measurement of the level of respiratory effort to trigger an arousal from sleep. The impact of COMISA on AT is not known. We hypothesized that a low AT is more common among COMISA than among patients with OSA without insomnia. Participants referred for OSA diagnosis underwent a type 3 sleep study and answered the insomnia severity index (ISI) questionnaire and the Epworth sleepiness scale. Participants with an ISI score ≥ 15 were defined as having insomnia. Sleep apnea was defined as an apnea hypopnea index (AHI) ≥ 15 events/h. Low AT was determined using a previously validated score based on 3 polysomnography variables (AHI, nadir SpO2and the frequency of hypopneas). OSA-only (n = 51) and COMISA (n = 52) participants had similar age (61[52–68] vs 60[53–65] years), body-mass index (31.3[27.7–36.2] vs 32.2[29.5–38.3] kg/m2) and OSA severity (40.2[27.5–60] vs 37.55[27.9–65.2] events/h): allp= NS. OSA-only group had significantly more males than the COMISA group (58% vs 33%,p= 0.013. The proportion of participants with a low AT among OSA-only and COMISA groups was similar (29 vs 33%,p= NS). The similar proportion of low AT among COMISA and patients with OSA suggests that the respiratory arousal threshold may not be related to the increased arousability of insomnia.