Background: The use of social media is expanding in medicine. More and more healthcare professionals, patients and advocates are using social media as a common platform to enhance communication.Methods: Each year American Society of Hematology (ASH) creates a hashtag (#) followed by year of the annual meeting (e.g. ASH 2014 had this hashtag: #ASH14) on Twitter. We conducted a retrospective study of annual meeting's hashtag use on Twitter for past 4 annual meetings using data from Symplur, LLC. Symplur is an online forum offering analytics of the global Twitter based conversations. Following hashtags were used for analysis, #ASH11, #ASH12, #ASH13 and #ASH14.Results: Overall there is an increasing trend for use of annual meeting's hashtag (see table 1). Last year's meeting generated over 72 million impressions. Number of tweets being sent out is doubling every year. More twitter users are engaging in conversations than the year before using annual meeting's hashtag. Last year almost 4000 individual twitter accounts were used during the annual meeting. Number of tweets per participant has stayed relatively constant over past four years. @ash_hematology remains the most commonly mentioned twitter handle every year since 2011. In 2014 itself, @ash_hematology was mentioned over 2000 times.Conclusion: Twitter is a very powerful tool that amplifies the content of scientific meetings. Use of twitter using meeting's hashtag is increasing every year at annual ASH meetings. This analysis provides a snapshot of twitter activity at the conference. Avenues for further research are: trend identification, "influencer" identification, and qualitative analysis. Interdisciplinary research should focus on evaluation methods that can assess the quality, value, and impact of tweeting.Table 1YearImpressionsTweetsParticipantsAverage tweet per participant201112,255,64631236065201218,153,7865,0948706201330,018,58012,23319426201472,433,27024,18539776 DisclosuresNo relevant conflicts of interest to declare.