An equation expressing the molar volume of deuterium to better than 0.1% up to a pressure of 1000 bar at temperatures from 273 to 423 K has been produced by fitting a modified van der Waals equation to experimental data. The equation fits all available data between 123 and 423 K but is also useful for extrapolation to at least 623 K at an estimated accuracy of 0.2%. This equation is more accurate than existing equations for deuterium below 1000 bar by about an order of magnitude.