Objective: The present study was designed to evaluate the associations between sleep duration and uncontrolled blood pressure in a hospital-based sample of middle-aged adults. Methods: Between March 2012 and December 2012, a cross-sectional survey was conducted among the hypertensive outpatients of Anzhen Hospital and a community hospital in Beijing, China. Eligible participants were adults aged 35-55 years with an established diagnosis of hypertension and had been on standard antihypertensive drug treatment for at least 6 months. An interviewer-led questionnaire was used to collect the participants' demographic, lifestyle and dietary information, as well as medical histories. Usual sleep durations were categorized as <7 h, 7-8 h and >8 h per night. Logistic regression models were used to assess gender-specific associations between sleep duration and uncontrolled hypertension, with adjustment for age, gender, family history, diabetes, smoking, alcohol consumption and physical activity. Results: A total of 3038 participants were finally investigated. Among them, 1569 (51.6%) patients had their blood pressure uncontrolled. In men, no significant association was found between sleep duration categories and uncontrolled hypertension. In women, compared with those sleeping <7 h, longer sleepers tended to have a lower risk of uncontrolled hypertension for sleeping 7-8 hours (odds ratio [OR] 0.537, 95% confidence interval [CI], 0.370-0.780) and sleeping >8 h (OR 0.316, 95% CI, 0.202-0.494), respectively. Conclusion: Modest associations between short sleep duration and uncontrolled hypertension were seen in middle-aged women but not in men in the hypertensive population.