['Although carpal tunnel syndrome is the most common compressive neuropathy, there is no comprehensive theory of its etiology. Because of the prevalence of night symptoms, we are interested in the role of sleep position in the causation of carpal tunnel syndrome.', 'We performed a case-control study comparing the prevalence of preferred sleep position in 68 cases and 138 controls. Analysis was stratified by age and gender and controlled for body mass index.', 'We found a strong and significant association between a preference for sleeping on the side and the presence of carpal tunnel syndrome in men and in women less than 60\xa0years of age. Body mass index was associated with carpal tunnel syndrome in women but not men.'] Is preferred sleep position on the side associated with carpal tunnel syndrome?