You should fill out the FAFSA. Even if you're fully funded to the extent where you will probably not need to take out loans, you may want the option of taking out loans later in the year if something happens that requires more money than you can afford. Also, some programs offer work-study over the summer for additional money (if your advisor has a grant, they might be able to buy up your work study so you work for them; if not, you may be able to do work around your department for extra cash). Also, some programs require that you do the FAFSA regardless of whether you plan on using the aid, for some administrative reason. The FAFSA doesn't take long if you have already done your taxes and have your 1040 available to reference. Because you'll be a grad student, you will not need to report your parents income, which makes it faster.