Influenced by a favorable environment, volunteer activities are integrated into medical education in the United States. Volunteer activities by medical students in hospitals are also becoming more common in Japan. With this background in mind, we performed a survey examining the nature of medical students' volunteer activities at the University of Hawaii in the United States and Saga University in Japan. By analyzing the percentages of students participating in volunteer activities and the location and content of the activities, we found that volunteer activities of medical students in Japan and the United States are strongly influenced by differences in the respective premedical education systems. We found that a premedical education that includes volunteer activities plays an important role in the United States. We suggest that further debate on premedical education that includes volunteer work is necessary for Japan to develop its own methods of medical education.