Whats wrong with this SQL statement?

I am trying to use a CASE statement in a WHERE clause, I have it to this point but when I try this I get the error "Incorrect syntax near the keyword 'END'".  And if I remove the single quotes surrounding the (companid=0....) I get a message saying the '=' is wrong.

I'm stuck... lol

p.s. This is the code in a stored procedure and all the variables are declared and correct.

BEGIN
	SELECT  
		count (DISTINCT (dbo.Member.ID)) AS mcount
	FROM 
		dbo.Member
	WHERE
		((SELECT count(billingid) FROM billingdata 
		  WHERE ((billingmonth>=@MONTH AND billingyr=@YEAR-1) OR (billingmonth<@MONTH AND billingyr=@YEAR)) AND (billingid=dbo.member.id)) >= 1
		) AND
		member.memberstatus=101 AND
		CASE
			WHEN @mtype='M' THEN '(companyid=0 AND departmentid=0 AND householdid=0)'
			WHEN @mtype='J' THEN '(companyid=0 AND departmentid=0 AND householdid>0)'
			WHEN @mtype='C' THEN '(companyid>0 AND departmentid=0 AND householdid=0)'
			WHEN @mtype='D' THEN '(companyid>0 AND departmentid>0 AND householdid=0)'
		END
END

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