Find Duplicate Values Between Two List In Excel?

I need help finding duplicates between two list that have 2 columns per list. There are two lists and four columns. I need to compare both list and find duplicates. Both list has Patient ID and Date and I need these two couple to match. One list is longer than the other (not sure is this makes a difference). I need help because there is no way I can do this manually, there's over 3K cells in one list. Please HELP! Thank you in advance.