not allowing invalid date in combobox

hello i have a userform with 3 comboboxes, one with the year one with month and one with date. There is a command button at the end. I want the command button to look at the month and date the use rhas selected and recognise if date is invalid eg. 30th. I know how to check for 1 box (if combobox2.value=Feb Then_ MsgBox....) but i dont know how to say, if combobox one has feb and combobox 2 has 30 then msgbox....

Any thoughts?

Many Thanks

Thankyou Norie it worked!