The aim was to develop a new instrument for measuring length of sleep as well as television and computer habits in school-age children. A questionnaire was constructed for use when children visit the school health care unit. Three aspects of the validity of the questionnaire were examined: its face validity, content validity, and construct validity. Test-retest reliability was assessed by giving the questionnaire twice, 2 weeks apart, to the respondents. The questionnaire was assessed as being reasonably valid, the test-retest results (n = 138) showing 90.4% of the estimates regarding bedtime on weeknights on the two survey occasions to lie within ± 30 min of each other, the test-retest agreement also being rather close (κ > .600) regarding both sleep and media habits. The instrument can be a valuable tool in a clinical setting, both for measuring sleep habits in a class and for discussing sleep with individual school children and their families.