Natural join problem

[John Meyer]

Two tables:

USERS:
USER_ID (PK)
. . .etc

TWEETS:
TWEET_ID (PK)
USER_ID (FK)

Trying to get the user information and the number of tweets each person has:

SELECT USERS.USER_NAME, COUNT(TWEETS.TWEET_ID) AS 'TWEETCOUNT' FROM 
TWEETS NATURAL JOIN USERS;

But it seems to be just rolling up all the information into one row.