Durable complete response rates for metastatic renal cell carcinoma (mRCC) and metastatic bladder cancer (mBC) are low despite new therapy. Palliative care focuses on life extension and quality of life (QoL), not cure. This study aims to investigate patients' perceptions of treatment outcomes in mRCC and mBC and to assess the influence of QoL and optimism levels on these perceptions. From March 15, 2023, to January 15, 2024, a multicenter, cross-sectional online survey was carried out, targeting patients diagnosed with mRCC and mBC. The survey comprised structured questions aimed at evaluating perceptions concerning disease cure, symptom improvement, daily activity performance, and life extension due to treatment. Additionally, to evaluate optimism and QoL, the European Organization for Research and Treatment of Cancer 30.3 QoL questionnaire and life orientation test were implemented. Study on patients' perceptions of treatment outcomes in metastatic kidney and bladder cancer shows high optimism, inaccurate cure beliefs. In total, 169 patients participated in the survey; the majority of the patients stated their general health status as good (72.2%) and excellent (13.6%). Patients who rated their overall health status as good-excellent had a higher median general QoL and optimism score compared with those who rated it as fair-poor. In all, 85.2% of patients considered the possibility of a cure very likely or likely. Most participants believed treatment could provide symptom relief (30.2% very likely, 49.1% likely), enhanced ability to perform daily activities (28.4% very likely, 55.6% likely), and life extension (32.5% very likely, 53.3% likely). Patients responding very likely and likely to these questions regarding treatment outcomes had higher QoL and optimism scores than those responding a little likely and not possible. The majority of patients with mRCC and mBC held inaccurate beliefs about treatment outcomes. Better QoL and optimism were associated with increased inaccuracy.