How can I see my follower's health?

Their health bar will show up only when you are in combat. Specifically, you and your follower need at least to hit an enemy or receive some damage for it to work.

Seems like this only works in combat. (or maybe only when they are damaged?)

I have seen the health bar when I put my cursor over them, but it only works when we're in the middle of a fight. Not sure if it is triggered by the combat, or by the fact that they have less than full health.

Given the usual caveats regarding using computing systems and variances of results...

In my experience so far, from release through the 1.2.12.0 update, I have not noticed any consistent pattern at all (sometimes it appears but normally does not). This includes:

• the bar appearing when in combat or not
• when their health is not 100% or not
• when they were recently damaged or not
• whether the player's char is in combat or not (I thought for a while I saw a pattern here... sadly it was not repeatable)
• when I am healing them, buffing, etc... or not, lol

Note: My rig is fairly high end and the settings are almost all set at the highest levels. As mentioned above, this has not changed at anytime though the different versions from final release which also includes before and after the "evisceration of larger address space, including use of more than 2 gigs of memory" as well as using the 4gb launcher.

If you're playing on the PC, the Floating Healthbars mod can add floating healthbars to any actor engaged in combat.