However, even if the Excel file is empty, thus containing only the headers, I end up with 13 as the number of rows. How come nCount is not properly initialized?

Michel....

Since you're using VS2005, you can utilize the new debugger to find out what's in the dataset. So set a breakpoint after the Fill statement, and put the mouse over the object reference to the dataset. You should see a small magnifying glass - click on that, and VS2005 should display the debugger visualizer for the dataset/datatable. Take a look at the contents.

KG