"Ghost" colmumn with primary key

Hello,
I have a table 'customers', with 2 records:

SELECT * FROM customers;
 customerID |  customerName
------------------+-------------------------
  myFriend   | myFriend's Name
      test       | testing user
(2 rows)

but when I'm asking about customerID column, I get the answer:

SELECT customerID FROM customers;
ERROR:  column "customerid" does not exist

What happens? I'm using PostgreSQL 8.1.3