The Slayer Helmet is a piece of useful equipment when doing Slayer tasks due to the fact that some tasks require protection from monsters. It nullifies the effects of Slayer NPC's, and removes the need to bring multiple items for Slayer tasks. It also gives a 15% bonus to Melee damage (bonus only applies on your Slayer task). The Slayer Helmet requires 35 Slayer and 10 Defence.
You can get a Slayer Helmet from the Slayer Point Shop for 1,000 Slayer Points. Since the Strykewyrm update, the Slayer Helmet has been made untradeable.