A large literature base on telemedicine exists, but the evidence base for telemedicine is very limited. There is little practical or useful information to guide clinicians and health policymakers. Telemedicine is often implemented based on limited or no prior formal analysis of its appropriateness to the circumstances, and adoption of telemedicine by clinicians has been slow and patchy. Formal analysis should be conducted before implementation of telemedicine to identify the patients, conditions and settings that it is likely to benefit. Primary studies of telemedicine tend to be of insufficient quality to enable synthesis of formal evidence. Methods typically used to assess effectiveness in medicine are often difficult, expensive or impractical to apply to telemedicine. Formal studies of telemedicine should examine efficacy, effectiveness, economics and clinician preferences. Successful adoption and sustainable integration of telemedicine into routine care could be improved by evidence-based implementation.