The Frogstar or Frog Star, in the fictional world of Douglas Adams' The Hitchhiker's Guide to the Galaxy, is said to be "the most totally evil place in the galaxy". Zaphod Beeblebrox learns this to his cost when he is taken there. When he asks if he is going to be fed, he is told that he will indeed be fed - into the Total Perspective Vortex.

The name "Frogstar" is a pun on the "Dog star", a common name for Sirius.