Retrieving Output Parameter From Stored Proc

I have difficulty reading back the value of an output parameter that I use in a stored procedure. I searched through other posts and found that this is quite a common problem but couldn't find an answer to it. Maybe now there is a knowledgeable person who could help out many people with a good answer.
The problem is that 
cmd.Parameters["@UserExists"].Value evaluates to null. If I call the stored procedure externally from the Server Management Studio Express everything works fine.
Here is my code:using (SqlConnection cn = new SqlConnection(this.ConnectionString))
{
SqlCommand cmd = new SqlCommand("mys_ExistsPersonWithUserName", cn);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add("@UserName", SqlDbType.VarChar).Value = userName;
cmd.Parameters.Add("@UserExists", SqlDbType.Int);
cmd.Parameters["@UserExists"].Direction = ParameterDirection.Output;
cn.Open();
int x = (int)cmd.Parameters["@UserExists"].Value;
cn.Close();
return (x>1);
}
 
 And the corresponding stored procedure:
 ALTER PROCEDURE dbo.mys_Spieler_ExistsPersonWithUserName
(
@UserName varchar(16),
@UserExists int OUTPUT
)
AS
SET NOCOUNT ON
SELECT @UserExists = count(*)
FROM mys_Profiles
WHERE UserName = @UserName


RETURN