When I call AddComment() worksheet creation slows dramatically. I can create a worksheet with a thousand rows in a second, but when I call AddComment on a cell more than a few dozen times it takes several minutes. I tried it with a MigrantRange and performance was still very slow. Can you provide a sample where you call AddComment for at least 20% of the rows, more than 200 times, that doesn't slow dramatically compared with when the AddComment() line is commented out? For example, with this code? http://mvc.syncfusion.com/demos/reporting/xlsio/DataManagement/Performance