Obesity is associated with a large variety of genetic and environmental factors. In order to understand the etiology of this condition and develop effective weight management programs, accurate acquisition of diet and physical activity data in free-living environment is essential. Currently, self-reporting is the primary method for data acquisition, but does not accurately reflect the true habitual behavior of individuals in real life. As a result, the lack of assessment tools to produce unbiased, objective data has significantly hampered the progress of obesity research. We propose a novel application of multimedia technology to study obesity. It will be based on electronic chronicle (or e-chronicle), a powerful multimedia data management technology which provides an easily accessible electronic memory of individual's experience and daily events. Specifically, we will develop a unified sensor device which is cosmetically pleasant and can be easily worn by patients. This device will consist of a set of physiological sensors and a miniature video camera. The data recorded will be uploaded to a powerful computer where extensive multimedia processing will be performed to remove human appearances in the video and organize information using the e-chronicle technology. Diet and activity related events will be automatically extracted, indexed, and organized into an easily accessible form, providing a new platform technology to study lifestyle, behavior, and environment that promises new understanding and effective treatment option to manage obesity. We propose a novel application of multimedia technology based on electronic chronicle to study obesity. We will develop a unified sensor device consisting of a set of physiological sensors and a miniature video camera to acquire field data. Diet and activity related events will be automatically extracted, indexed, and organized, providing a new platform technology to study lifestyle, behavior, and environment that promises new understanding and effective treatment option to manage obesity.