I had the same problem you did, thought I'd post my solution even if it's too late to help you. In the Pattern Expression you should not be returning a pattern, but rather a string from which a pattern will be made. For example, in my report I wanted numbers formatted as "#,##0.00;(#,##0.00)" but when the field label was "Net Invoiced" i wanted the output to be bold. So, in Pattern Exp. I put: $F{label}.matches("Net Invoiced")? "<b>#,##0.00;(#,##0.00)</b>":"#,##0.00;(#,##0.00)" Hope that helps someone!