The purpose of this study was to study Diabetes Mellitus patients self-care behaviors and to determine family social support patterns which affected Diabetes Mellitus patients self-care behaviors. These behaviors include dietary control, medication intake, daily exercise and complications arising from aspects of prevention. A total of 20 patients, who attended the outpatient clinic of a Bangkok hospital, were evaluated in this case-study research. The data were collected through indepth interviewing in a 5-month period. The results of this study revealed social support influenced self-care behaviors as seen in 3 patterns: 1. Patients would have close familial relationships and reported beliefs and thoughts congruent with family numbers. This particular pattern appeared to enhance the patients ability to effectively adjust their self-care behaviors through strict dietary control, and ingestion of doctor-prescribed medicine only. 2. Some patients received familial social support, but their self-care behaviors were influenced more by their own beliefs and experience, which contrasted with their family numbers. There were patient-family differences in term of dietary control and medication intake, thus these patients did not control their diets. They sometimes would use herbal drugs besides the hospital medicine. 3. Another group lacked social support due to poor relationship among family numbers. This group of patients reported tension and anxiety. Their self-care behaviors were influenced by their own beliefs and experience, and thus, they reported dietary control and medication selection was affected. Specifically these patients often used hospital medicine as well as a wide range of herbal drugs. The study showed that most patients followed strict dietary control pattern, followed by a not-strict dietary pattern, and finally, an uncontrolled dietary pattern. Interms of medication intake, it was found that most patients simultaneougly used herbal drugs and hospital medicine. These patients did not exercise regularly, except ,when enjoying in household activities or office work. They reported no interest in exercising. Regarding foot care patients reported no change in foot cleaning (pre-and post illness), although they would pay more attention if a wound developed because they feared complications.