The linear thermal expansivity of polycrystalline silver iodide has been measured with a "Fused-Quartz Tube" apparatus in the temperature range 170 - 500 °C, the mean linear thermal expansion coefficient being αt180=(2.607 + 0.00182 t) 10-5 (°C-1). An irregular change in the thermal expansivity was found close to 432 °C where an order-disorder transition has been reported.