I Have Black Mold In My Bathroom Of My Apartment. May I Break My Lease Legally?

I think you are going to have to make your landlord fix it, if it is in the wood and structure of the walls. Other than that, you should go and talk to the landlord/tenant board. Hope this helps, good luck.

Don't know where you live, but do know that in some areas of the world, you must first notify the landlord with a written complaint. Would make a copy of it and then send it out Registered or Return Receipt Requested mail. The landlord has so many days to fix the problem, then if he/she fails to do so, you can break your lease.
Would inquire with your local housing authority/government to find out for sure, before breaking the lease.

I'm not sure about that, but what you could do if they refuse, or take wayyy too long to remedy this problem, absolutely you can call the Board of Health. They will contact your landlord immediately, and then follow up to make sure that he has fixed your bathroom. Mold is a health hazard. Years ago when I got my first apt., I had the same problem. The Board health took care of it for me. After months and months and months of pleading with the landlord for a new bathroom, 3 days after my call to the board of health, the apartment people came in and starting re-doing my bathroom.  ;o)

After you send them notice by certified mail of the problem they have to fix it, and after a while goes by with the problem not fixed you can.