comparing two list using class

I have list which will select all field's from sql database and store it in a list

I have another list with the newly downloading file with their file ids.(File ID are unique)

Now I want compare these two list so that the newly downloaded values will be saved to database only if the fileId is not existing in the database.ie File ID 5 is there in database and File ID 5 is downloaded again by the window service,It will not be saved in the database, Hence there will be no duplicate records with same file ID.Thank u very much
Thank You
Checking from db    
 cmd1.Connection = con1 
 cmd1.CommandText = "select FileID from FileMaster"   
  drd1 = cmd1.ExecuteReader     If drd1.HasRows = True Then
        Do While drd1.Read      ...