OBJECTIVES: : The present study aimed to determine the proportion of physicians in Japan who use clinical practice guidelines, as well as factors influencing this choice. METHODS: : We conducted an on-line cross-sectional survey throughout Japan on general internists, gastroenterologists, cardiologists, endocrinologists and general surgeons, including gastrointestinal or breast surgeons, who registered for marketing research. Questions addressed their usage of CPGs in practice, education, and research, as well as their attitudes toward CPGs. We then investigated associations between usage and characteristics of the respondents. RESULTS: : We received responses from 1342 physicians, 1222 (91.1%) of whom were male (mean age (SD), 46.5 (9.6) years). The proportion of respondents who always or often use CPGs in several practice settings, such as when providing explanations to patients based on CPGs, ranged from 27.7% to 54.6%. Among them, 822 respondents (61.3%) applied 1 to 4 CPGs, and 381 (28.4%) applied 5 to 9. Usage differed according to age group, subspecialty, and workplace. After multivariate adjustment, the mean probability (95% confidence interval) of a high usage of CPGs when providing explanations to patients was 65% (60% - 71%) and 40% (30% - 50%) for those aged < 40 y and ≥ 60 y, respectively, 44% (38% - 50%) for general internists, 65% (59% - 71%) for surgeons, and 51% (46% - 57%) and 65% (58% - 72%) for those working in clinics and university hospitals, respectively. Attitudes towards the trustworthiness and convenience of CPGs were associated with usage, although this was unable to explain all differences in usage among subgroups. CONCLUSIONS: A substantial proportion of Japanese physicians use CPGs in clinical practice. Age, subspecialty, and workplace were independently associated with CPG usage. This should be considered during the process of CPG implementation.