By appearance this metal hat is simply a typical helmet. By test, it will radiate an indeterminate dweomer. 

Once placed upon the head, however, its curse immediately takes place, and the alignment of the wearer is radically altered — Good to Evil, Neutral to some absolute commitment (LE, LG, CE, CG) as radically different from former alignment as possible. 

Alteration in alignment is mental and, once effected, is desired by the individual whom the magic changed. 

Only a wish, or alter reality, can restore former alignment, and the affected individual will not make any attempt to return to former alignment. 

If a paladin is concerned, he or she must undergo a special quest and atone if the curse is to be obliterated. 

Note that once a helm of opposite alignment has functioned it loses all of its magical properties.