Objective: Sarcopenia is known to influence cancer-related complications and overall survival. However, the effect of cancer treatment on the development or progression of sarcopenia is relatively unknown. The primary aim of this systematic review was to determine the prevalence and development of sarcopenia among people with bladder cancer. Data Sources: A systematic search was performed in PubMed, Web of Science, and EMBASE. Studies with ≥2 assessments of sarcopenia were eligible for inclusion. Five retrospective cohorts were included with a total of 438 participants. The baseline prevalence of sarcopenia across studies varied from 25% to 69% and post-treatment prevalence from 50% to 81%. The average loss of muscle mass was 2.2% to 10% during a time course of 3 to 12 months. Conclusion: The prevalence of sarcopenia markedly increased during cancer treatment in patients with bladder cancer. Further research into the effect of different treatment regimens on the development of sarcopenia, and how these changes might affect functional capacity and survival is needed. Implications for Nursing Practice: The development of sarcopenia is important to understand because of its negative affect on quality of life, complications, and mortality. Further, understanding how sarcopenia develops during treatment could potentially strengthen nurses’ future care plans for patients with bladder cancer.