This study investigates patterns of on-line communication between physicians and patients on the consulting board of the KingNet WebHospital in Taiwan. The dermatology, urology, gynecology and pediatrics departments, which all have frequent physician-patient interaction on KingNet, were selected as samples. After conducting content analysis of total 600 on-line messages between physicians and patients from these four departments, we classified patients’ questions into four categories: “Symptoms and Diseases,” “Medications or Treatments,” “Tests or Diagnostic Procedures,” and “Prevention.” We also analyzed physicians’ responses and classified them into three types: ignore, partially-fulfil and fulfil. While questions involving “Symptoms and Diseases” were the ones most commonly raised by patients in all four departments, they were also the ones that most physicians ignored or answered only vaguely. To understand the possible causes of this gap, interviews were conducted with the physicians. The results show that, for physicians it is difficult to answer such questions on-line due to uncertainty of medical treatments, restrictions imposed by medical regulations, the possibility of medical disputes, and the perception gap between patients and physicians. Consequently, physicians tend to either offer “partial” suggestions or ask patients to go to hospital for further examination.