Background: Japan has an extremely large number of hot spring facilities, with more than 27,000 natural spring sources across the country. Despite the high usage of hot springs for leisure in Japan, almost no studies have investigated the general public’s utilization of hot springs at non-medical facilities as a form of alternative medicine. The aim of this study was therefore to elucidate the current status, including frequency and purpose, of hot spring utilization as an alternative medicine. Methods: In January 2011, we conducted an online self-administered questionnaire survey on balneotherapy utilization of 10,400 ordinary citizens (men and women, 5,200 each) aged 20 to 69 years who were registered as consumer reviewers with an Internet survey company. Results: Among 10,400 Internet consumer reviewers, 3,227 responded to the survey (response rate, 31.0%), of whom 3,212 provided unambiguous survey responses and were subsequently included in this study. The results revealed that 177 subjects (5.5%; 85 men, 5.3%; 92 women, 5.7%) had utilized balneotherapy (in the form of bathing, drinking, and/or inhalation) at a non-medical facility in the previous month. Among participants who had consulted a physician in the previous month, 51 (9.1%) had utilized balneotherapy, compared to 41 (3.9%) among those who had not, revealing significantly higher utilization of balneotherapy among those who had consulted a physician (p<0.001). Only 7 men (8.2%) and 1 woman (1.1%) consulted a physician prior to balneotherapy, and 8 men (9.4%) and 2 women (2.2%) received a physician referral. Conclusions: This online survey of balneotherapy utilization among the general public in Japan revealed that among those in the study population with recent experience of balneotherapy, few had consulted or obtained a referral from a physician prior to utilization.