BACKGROUND: Twitter is the most popular form of microblogging that is being utilized in public health to engage audiences and to communicate health-related information. Although there is some research showing the various forms of Twitter use in public health, little is known about how individual public health professionals are using their personal Twitter accounts to disseminate health information. OBJECTIVE: The purpose of this research was to categorize public health professionals' tweets to evaluate how individual public health professionals are furthering the mission of public health. METHODS: Twitter accounts held by public health professionals were identified, and researchers proceeded to record 6 months' worth of each individual's Twitter feed. During the 6-month period, a total of 15,236 tweets were collected and analyzed using the constant comparison method. RESULTS: A total of 23 tweet categories among the 15,236 tweets were initially identified. Some of the most common topics among the 23 categories included the following: health nutrition (n=2008), conferences (n=815), Ebola (n=789), Affordable Care Act (ACA)/health care (n=627), and social justice (n=626). Each of these categories were then stratified into one of four themes: (1) informing and educating, (2) monitoring health statuses and trends, (3) social justice, and (4) professional development. CONCLUSIONS: Using Twitter, public health professionals are helping dispel misinformation through education and by translating technical research into lay terms, advocating for health inequalities, and using it as a means to promote professional development.