Tensile specimens of cast polymethyl methacrylate of five different molecular weights varying from 90 000 to 3 160 000 were broken by static loading and the fracture surfaces compared. The fracture appearance was fairly constant for a given molecular weight but there was a continuous development of certain features and a retrogression of others with changes in molecular weight. The series which was developed by varying the molecular weight was similar in appearance to that developed by Zandman by varying the rate of loading of polymethyl methacrylate. The higher molecular weight specimens corresponded in appearance to those obtained at the lower rates of loading. In the higher molecular weights, failure by ``separation'' was most marked whereas fracture by ``pulling out'' of polymer masses became more important at the lower molecular weights.