You can file a bankruptcy without tax returns but if you have unfiled tax returns it may be in your best interest to file them before you file as opposed to right after you file for bankruptcy. It is in you best interest to have your tax returns filed prior to the filing of your case. This is especially if you are looking at filing a Chapter 13 bankruptcy. You want to know how much tax you will be required to pay on during a repayment plan that you will be proposing to the bankruptcy court. With out a firm number on the amount of outstanding tax debt you owe the court will not approve your proposed bankruptcy plan. Your bankruptcy in a Chapter 13 will not be approved unless you have your tax return filed. To decide if you should file your tax returns or file for bankruptcy first, remember that in order to know how your taxes, penalties, and interests will be treated your tax returns have to be prepared.
In a Chapter 7 bankruptcy case you will need to know what your possible tax refund might be prior to the filing of the case so it usually a good idea to file your tax returns prior to the filing of a case. In most cases tax debt survives the filing of a bankruptcy so any taxes you owe will still be owed even if you file for bankruptcy. But as I said the refund is different.
Planning the filing of your bankruptcy is an important step in the process and is why I always suggest you work closely with an experienced bankruptcy lawyer. Not only will the process go much smoother for you a bankruptcy attorney may be able to come up with legal ways to help you protect more of your asserts including the proceeds from a tax refund.