Abstract: Disclosed is a vacuum breaker and backflow prevention device for a faucet comprising a body member having a tubular outlet portion integrally joined by a web to a tubular inlet portion of larger diameter than the outlet portion, the web having a plurality of vent holes therethrough and peripherally supporting a flexible, resilient diaphragm and overlying plate member. The plate member has an outer region provided with a plurality of through holes and a central depending shank portion extending through a central hole in the diaphragm. The tubular inlet portion has internal screw threads for attachment to a faucet outlet member whereby the plate and diaphragm are retained in the tubular inlet portion by the outlet member.