Insomnia, the most common sleep disorder, is 40% more likely to occur in women than in men. However, insomnia often remains unnoticed in general hospitals and only scant data exists regarding insomnia's sex-differences in hospitalized patients.

This study explored in medical inpatients potential sex differences in insomnia and investigated which, if any, self-reported insomnia-related complaints were most sex-differentiated.

Five-hundred patients admitted to medical wards of three general hospitals were randomly selected during 2010–2011. All patients completed the Athens Insomnia Scale (AIS), a standardized self-assessment instrument based on ICD-10 criteria for insomnia. A mixed regression model of ordinal data explored potential sex differences in specific AIS questions.

As expected, total AIS scores, controlled for age, were significantly higher in hospitalized women, which were 1.5 times more likely to score above the AIS cut-off score than men. the statistical analysis indicated significant sex differences in self-reported insomnia complaints. in the entire patient sample, women were generally more likely to complain about frequent awakenings during the night, reduced sleep duration and quality, reduced functioning and well-being during the day and increased sleepiness. the observed sex differences specifically in awakenings during the night, reduced sleep quality and sleepiness during the day were also identified in the sample of patients who screened positively for insomnia.

Women admitted in general hospitals complain heavier than men regarding frequent awakenings during the night, reduced sleep quality and day sleepiness. These findings should be taken into account when assessing insomnia in medical inpatients.