Embodiments disclosed herein are directed to negative pressure treatment systems and wound dressing systems, apparatuses, and methods that may be used for the treatment of wounds. In particular, some embodiments are directed to improved wound dressings comprising a number of viewing portals that facilitate observation of wound tissue or healthy skin underlying the wound dressing. Some embodiments of the viewing portals are provided by forming through holes in internal dressing layers including absorbent material and transmission material, optionally by providing a plug material within the through holes, and by providing translucent or transparent cover layer and tissue contact layer materials.