The susceptibility of metastable 304L to embrittlement in a high-pressure gaseous hydrogen environment was studied from the viewpoint of changes in mechanical properties. The high pressure hydrogen gas leads to deterioration of mechanical properties, which may be accelerated by the presence of surface defects. The tensile specimens were cut with different machining parameters to change the density of the different defects caused by the machining. The maximum dislocation density caused by machining, rather than the maximum strain-induced martensite increased the sensitivity to hydrogen embrittlement.