Conventionally produced high pressure die-cast (HPDC) components are not considered to be heat treatable because gases entrapped during the die-casting process expand during solution treatment causing unacceptable surface blistering. Components may also become dimensionally unstable. Both these effects prevent the heat treatment of die-castings as these phenomena are detrimental to the visual appearance, mechanical properties and utilisation of the component. Recent work has revealed a process window in which HPDC aluminium alloys that are capable of responding to age hardening may be successfully heat treated without encountering these problems. As a result, improvements of greater than 100% in the tensile properties are possible, when compared with the as-cast condition. The new heat treatment schedules are described for HPDC parts of different size and shape, the role of chemistry on ageing is discussed and microstructural development during heat treatment examined.