Purpose <p>The objective of this study was to determine the primary stability of an uncemented humeral implant when used for acute proximal humeral fractures.</p> Methods <p>A prospective study that includes consecutive proximal humeral fractures treated with an uncemented rTSA. Three measures were obtained to assess the stability of the implant: the retroversion, the humeral stem height and the varus/valgus alignment of the humeral component. The three measures were done in both the CT scan obtained 24&#xa0;h after surgery, and the CT scan obtained at the 6&#xa0;month follow-up. Among the patient sample included, five patients were randomly selected to be treated with a rTSA with a cemented humeral stem. They were used as the control. The difference between both CT measures were recorded.</p> Results <p>A total of 27 patients were included. There were 22 females and 5 males, with a mean age of 74.2. The mean difference in retroversion in the humeral component in the patients with the uncemented stem between both CT was 0.4º (SD 5.1º). However, the mean difference in retroversion in the humeral component in the patients with the cemented stem was 4.4º (SD 5.2º). There was no significant difference between them (<i>p</i> = 0.155). No other significant difference was found between uncemented and cemented humeral stems regarding humeral stem height (<i>p</i> = 0.574) nor varus/valgus alignment (<i>p</i> = 0.287).</p> Conclusion <p>The findings of this study suggest that uncemented humeral stems provide satisfactory primary stability in rTSA used in acute proximal humeral fractures whenever there is no comminution of the proximal humerus and/or metaphyso-diaphyseal extension of the fracture.</p>