Sleep questionnaires are useful tools both for screening patients who require medical tests and for epidemiologic research. The Pediatric Sleep Questionnaire (PSQ) has two versions: a shorter one, which has been validated for sleep-related breathing disorders, and an extended version, which deals with a wider range of sleep disturbances. The PSQ was translated into Spanish and its reliability was determined by means of test-retest and internal consistency methods among a random sample of 99 patients. Ninety-one percent of the questions showed good concordance, following the criteria established in the test- retest method. Internal consistency was good in parts A (nighttime and sleep behavior) and C (items for inattention and hyperactivity) of the questionnaire but was weak in part B (daytime behavior and other possible problems). Therefore, the reliability of the questionnaire can be considered to be adequate except for the internal consistency of part B. The Spanish version of the PSQ is a suitable tool both for screening patients who require medical tests and for epidemiological research.