Healthcare institutions including hospitals and clinics are increasingly using social media platforms, such as Twitter, to raise awareness in the community about health and wellness topics. In line with this trend, this study seeks to understand how three leading medical centers in the USA use Twitter to share educational content about medical conditions, treatments, preventive measures and other health-related topics. A sample of tweets posted by Cleveland Clinic, Johns Hopkins Hospital and Mayo Clinic during a 6-month timeframe was collected and thematically analyzed. The first analysis, which focused on eight popular health topics, showed that diet and cancer were consistently the most and diabetes was the least frequently used topics in the tweets. The second analysis, which drew upon the health belief model to understand the educational themes embedded into the tweets, revealed that the three institutions mainly provided general health advice and information in their tweets and paid less attention to causes and consequences of diseases, preventive strategies and patient success stories. Accordingly, it is recommended that healthcare institutions adjust their tweeting activities and align them with society’s health education needs. Such revised content strategies can help medical institutions achieve their health promotion goals more effectively.