To develop a single-administration instrument yielding equivalent measures of sleep to those obtained from a formal (2-week) sleep diary. A single-administration Sleep Timing Questionnaire (STQ) is described (and reproduced in the Appendix). Test-retest reliability was examined in 40 subjects who were given the STQ on two occasions separated by less than 1 year. Convergent validity was measured both by comparing STQ-derived measures with objective measures derived from wrist actigraphy (n=23) and by comparing STQ-derived measures with other subjective measures derived from a detailed 2-week sleep diary in two nonoverlapping samples (n=101, 93). Correlations of STQ measures with age and morningness-eveningness (chronotype) were also examined. The analyses used sample sizes of 40, 23, 101, and 93 (both genders, overall age range 20y - 89y). Most subjects were healthy volunteers; some Study 4 subjects were patients (enrolled in research protocols). Test-retest reliability for the STQ was demonstrated for estimates of bedtime (r=0.705, p<0.001) and waketime (r=0.826, p<0.001). Convergent validity using wrist actigraphy was demonstrated by correlations of 0.592 (p<0.005) for bedtime, and of 0.769 (p<0.001) for waketime. Diary studies indicated STQ bedtime and waketime data to be highly correlated (at about 0.8) with those obtained from a formal 2-week sleep diary. The STQ also provided data on estimated sleep latency and wake after sleep onset (WASO), which correlated reliably (at about 0.7) with average nightly ratings of these variables from a 2-week sleep diary. Mean estimated values of sleep latency and WASO from the two instruments were within 1 minute of each other. STQ-derived bedtimes and waketimes correlated with both age and chronotype in the expected direction (older subjects earlier, morning types earlier). The STQ may be a reliable valid measure of sleep timing that could provide a time-efficient alternative to traditional sleep diaries.