I tried the following:

declare @table table (id int, [name] varchar(10), gender char(1))

declare @MaleNames varchar(255)

insert into @table values (1,'John','M')

insert into @table values (2,'Sue','F')

insert into @table values (3,'Jane','F')

insert into @table values (4,'Mark','M')

insert into @table values (5,'Bill','M')

insert into @table values (6, null,'M')

insert into @table values (7,'Dingbat','M')

select @MaleNames = IsNull(@MaleNames + ', ','') + [name] from @table where gender = 'M' ORDER BY name

Select @MaleNames as MalePatients

Output is:

Bill, Dingbat, John, Mark