Objective: Using 12 years of administrative data, we assessed the trends in the use of breast conserving surgery (BCS) before and after the release of clinical guidelines on BCS in Japan (published in 1999 and updated in 2005.) Methods: We used a database from the Quality Improvement/Indicator Project that involved 40 teaching hospitals in Japan. Data on all discharged cases were collected from these hospitals from 1995. We then selected female operable breast cancer patients who were admitted to five of these hospitals from January 1996 through September 2007 (n = 1,971). A multiple regression analysis was performed to examine whether the proportion of the use of BCS after publication of guidelines was higher than that before publication, after adjusted for the effects of patient's age, comorbidity status (Charlson Comorbidity Index), hospital, and time period of admission. The Hosmer-Lemeshow test was conducted to assess the goodness-of-fit of the model. Results: The proportion of BCS use increased from 16.1% in 1996 to 62.2% in 2007. Multiple logistic regression analysis revealed that patients who were <50 years old (P <0.001) and had no comorbidity (P <0.001) were significantly more likely to receive BCS. The proportion of BCS use has been substantially higher since 2001, two years after the BCS guidelines were published in Japan. Significant practice variations of BCS use were also confirmed among hospitals. Conclusion: This study confirmed the lag time between guideline publication and change in practice of BCS use. We further need to examine the potential barriers to guideline adoption related to physicians' knowledge and attitudes as well as external barriers including patient-, guideline-, and environment-related factors, to explain the reasons of change in the use of BCS over ten years.