Must my landlord tell me if there was a mold problem?

The law is not clear on this issue, and laws differ from state to state.  A landlord must provide you with a safe living space. That means that any environmental conditions that could adversely affect your health must be fixed.  The problem with mold is that it is a natural organism that exists in every home to some extent.  Pacific IAQ has been on both sides of this legal issue and more often than not, the law favors the tenants when a landlord fails to address mold and water damage issues.