Hidden Accessible Fieldsets

It is good to group checkboxes and radio buttons for accessibility purposes.  The fieldset and legend elements allow developers to group related controls and labels.  Grouping elements make it easier for users to understand their purpose.  Screen readers will detect fieldsets and inform the user of their purpose via the legend tag.  Keep in mind that an elaborate interface may not transfer logically to someone using a screen reader.   With CSS you can cater to both worlds.  You can utilize fieldsets but also hide them if they are not visually pleasing.  A hidden fieldset is completely detectable by a screen reader.

Here is a snipplet of CSS that will hide the fieldset and remove the legend indent.
If you want to hide the legend as well then alter the CSS as so:
See a DEMO

Enjoy.