Femoral stem fractures in total hip arthroplasty (THA) are a problem in clinical practice that results in great morbidity and high cost of revision hip surgery. Stem fractures are multifactorial events that are usually related to a combination of factors that increase the mechanical stress on the stem or decrease the mechanical strength of the implant. Failure analyses of hip prosthesis have identified that the presence of inadequate grain size may lead to implant failure. The aim of this article is to develop a rational to set specific sites to perform grain size measurements along stems used in THA as well as appropriate procedures to evaluate the heterogeneity of the microstructure related to the grain size distribution. In the present study, nonmodular femoral stems from three manufacturers with different wrought materials were chosen: stainless steel ISO 5832-1 (Manufacturer I), high nitrogen stainless steel ISO 5832-9 (Manufacturer II), and cobalt-chromium-molybdenum alloy ISO 5832-12 (Manufacturer III). The results of this study showed a great variability of grain size number depending on the cross section and fields evaluated. Therefore, the current technical standards for evaluating THA stems need to be modified. Analyses of grain sizes at different cross sections and inside each cross section of the stem is necessary to ensure the safety of hip stems.