Cthulhu Companion is a supplement with information on prisons, insanity, Mythos creatures, notes on the Necronomicon, and poetry by H.P. Lovecraft, and contains three short scenarios.
Jon Sutherland reviewed Cthulhu Companion for White Dwarf #51, giving it an overall rating of 7 out of 10, and stated that "In conclusion, this tome is really of use only to the Keepers of Arcane Knowledge and given that this does not set out to fundamentally change any of the basic rules themselves, again this will limit appeal. The scenarios are quite good and altogether, this represents a predictable package and is reasonable value for money."
- Different Worlds #36 (Sept./Oct., 1984)