Mixtures of argon and neon have been experimentally studied under high pressure. One stoichiometric compound, with ArNe2 composition, is observed in this system. It is a Laves phase with a hexagonal MgZn2 structure, stable up to at least 65 GPa, the highest pressure reached in the experiments. Its equation of state follows closely the one of an ideal Ar+2Ne mixture. The binary phase diagram of the Ar-Ne system resembles the diagram predicted for hard sphere mixtures with a similar atomic radius ratio, suggesting that no electronic interactions appear in this system in this pressure range. ArNe2 can be a convenient quasihydrostatic pressure transmitting medium under moderate pressure.