It's difficult to fix your problem with such little info, but... i beleive you are experiencing a texture resolution problem with your displacement map. Multiple things can cause this. Low resolution maps, Not setting yout tesselation correctly, Using maya to displace for mental ray and so on. Please post a picture or the file so we can better help you.
And after calming me down with some orange slices and some fetal spooning,
E.T. revealed to me his singular purpose.
--TOOL, 10,000 Days---