This paper examines herding behavior among Hong Kong investors using announcements of the opening of new casinos in Macau. The results show that there is a difference in the herding behavior toward these “Macau concept” stocks before and after the change in investment sentiment regarding Macau. Similar results are also revealed for the impact of announcements related to the Macau concept. Furthermore, investors in general herd more on selling than on buying upon a corresponding announcement. The evidence that is documented in this paper also suggests that there is herding around exceptional price and trading volume movements in the trading of Macau concept stocks.