tymjr, The difference between the two IMO is that trailing stops bunch up where traditional stops are scattered about. Say a stock is rallying along nicely. Stops keep inching higher and higher, more stops are added as other trade. Say this goes on for a couple of months and thus potentially you can get into a situation where there are a large number of stops roughly with the same trigger price. Then bad news, the stock gaps down and the move gets exagerated by a flood of market orders. In terms of network capacity and potential regulatory enquiry I see this as a major difference.