While you may have organized as a state level LLC, you apparently made an election to be taxed as an S corporation. As a result, you need to track your basis.
While you may not have any stock, since you organized as an LLC, you have units. So in your case, your "stock" is a unit. The end result is the same; tracking your basis; regardless of units or stock.
*A reminder that posts in a forum such as this do not constitute tax advice.
Also keep in mind the date of replies, as tax law changes.
