Objective:This studywas conducted to investigate the comorbidity of obstructive sleep apnea syndrome (OSAS) in patients with insomnia.Methods: Medical records were collected from Department of Sleep and Psychology, Institute of Surgery Research, Daping Hospital.Chi-square test was used to detect whether statistical differences of comorbidity exist between different gender, age and body mass index(BMI) groups.Binary logistic regression was used to calculatetheodds ratio (OR) of BMI to comorbidity.Mann-Whitney U test was applied to explore differences of sleep parameters between insomnia patients with and without OSAS.Results:A total of 2094 patients (802 men and 1292 women) with insomnia have been collected.The incidence of comorbiditywas 23.69% in total, and men has a significant higher rate of comorbidity than women (38.28% and 14.63% respectively, P<0.001).Three age groups, that are 20-39, 40-49 and 50-79years old, were divided in male and female patients separately.Comorbidity was positively correlated with age both in men and women (male: P20-39,40-49<0.01, P40-49, 59-79>0.05, P20-39, 50-79<0.001; female: P20-39, 40-49<0.001, P40-49, 59-79<0.001, P20-39, 50-79<0.001).Similarly, prevalence of comorbidity was increased with BMI in the same age groups.Compared to insomnia-only patients, the insomnia and OSAS patients showed increased number of arousals (Pmale<0.001, Pfemale<0.05), duration of non-REM sleep stage 1 (N1; Pmale<0.001, Pfemale<0.05), and decreased sleep latency (Pmale<0.001, Pfemale<0.05) in both genders.Meanwhile,total sleep time (P<0.05) and duration of N2 (P<0.05) was decreased in female patients with comorbidity than female insomnia-only patientswhile in male patientsthedecreasein duration of N3(P<0.01) was observed.Conclusion:Our results suggested that male patients with insomnia had a higher incidence of OSAS than female patients.Co-occurrence of OSAS in insomnia patients was increased with age and BMI both in men and women.Also, we found that sleep architecture between patients with and without OSAS was significantly different in both genders.