Background. Habitual short (HSS) and long sleeper (HLS) were very interesting but under-research area. / Conclusion. Our study suggested that sleep duration of human being has marked inter-individual variability with existence of extreme sleepers at both ends. Throughout different phases of the study, there was a consistent negative relationship between sleep duration and socio-economic status. Our finding of unique personality profile between short and long sleepers supported the hypothesis that different personality trait (neuroticism trait) might mediate between sleep duration and socioeconomic variables. Further studies are indicated for investigating genetic as well as biological correlates between personality traits and sleep duration. / Method. Three phases were involved in this research to explore epidemiological, psychological, and PSG characteristics of HSS and HLS. / Phase three: 72 subjects (23 HSS, 41 HNS, and 8 HLS) were assessed by two nights PSG to be followed by multiple sleep latency test (MSLT). 37 subjects (6 HSS, 21 HNS, and 10 HLS) were assessed by four-day Actiwatch. In the first night of PSG assessment, HLS had lower sleep efficiency and longer sleep and REM latency than HSS and HNS. In the second night, REM density in HLS was higher than HSS and HNS. In MSLT, HSS (50.0%) was more likely to have mildly short sleep latency than HLS (0%). Multiple regression of these healthy sleepers suggested that shorter sleep duration was found in those subjects (a) attaining higher education level; (b) suffering from higher life stress; (c) having more sleepiness; and (d) having less neuroticism. / Phase two: 252 subjects attended the face-to-face clinical interview. Among them, there were 33 HSS-7 and 25 HLS-9. After controlling gender and age, HSS had more chance to earn more money, live in larger house, drank more alcohol, and lower neuroticism than HLS. / Result. Phase one: Brief sleep questionnaires with consent were administered to parents of students in 13 primary schools in 2003, and 10381 parents returned their questionnaires (response rate ≈ 67.9%). 593 subjects were excluded because of their incomplete information. Altogether, 9788 subjects were considered as eligible subjects that represented noninstitutionalized Chinese middle-age residents in Hong Kong (47.0% men vs 53.0% women, mean age: 40.9 years +/- 4.9 years [SD]). There were 322 (3.3%) HSS-7 (≤7 hours), 1415 (14.5%) HLS-9 (≥9 hours), and 481 (4.9%) HLS-10 (≥10 hours). HSS had more chance to attain higher education level, earn more money and drank more tea/coffee than HLS. / Zhang Bin. / "May 2005." / Advisers: Y. K. Wing; S. O. Chan. / Source: Dissertation Abstracts International, Volume: 67-01, Section: B, page: 0177. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 155-193). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.