An audit opinion that is not considered ‘clean’ is one
that has been modified. Auditors issue a modified
audit opinion if they disagree with management
about the financial statements. In practice this may
be unusual as the company will typically make the
necessary amendments to the financial statements
and disclosures rather than receive a modified
opinion. The auditors will also issue a modified
opinion if they have not been able to carry out all the
work they feel is necessary, or if they have been
unable to gather all the evidence they need.