Ribosomal S6 kinase 4 (RSK4) has been established as an oncogenic driver in several malignancies, although its clinical significance in bladder cancer remains undefined.<h4>Objective</h4>To evaluate RSK4 protein expression in bladder cancer specimens and assess its association with clinicopathologic features and patient outcomes.<h4>Design</h4>RSK4 expression was analyzed by immunohistochemistry in a retrospective cohort of 143 bladder cancer specimens, including 93 cases represented in a tissue microarray. The gene discussed is RPS6KA6; the disease is urinary bladder carcinoma.