Emergence of malignant ureteral obstruction (MUO) has been reported as a sign of poor prognosis; however, the distribution of survival time in patients with MUO is considerably wide, and no risk classification score has been constructed. To evaluate whether a novel risk classification score for overall survival that we previously developed, is effective in a large cohort. Investigator-initiated, prospective, multicenter diagnostic/prognostic study was conducted. Patients with MUO were divided into three risk groups based on the score calculated using four prognostic factors (PLaCT: Primary site, Laterality, serum Creatinine level, and Treatment for primary site) at the first visit, and prospective follow-up was performed. Overall survival and ureteral stent failure-free survival of each risk group were compared. In total, 300 patients with 21 different primary sites were enrolled. The numbers of patients in good, intermediate, and poor risk groups were 105, 106, and 89, respectively. Median survival times of patients in good, intermediate, and poor risk groups were 406, 221, and 77 days, respectively (P < 0.0001). In 217 patients with ureteral stenting, median ureteral stent failure-free survival times of good, intermediate, and poor risk groups were 385, 183, and 57 days, respectively (P < 0.0001). Limitations include the limited ethnicity and the extended duration of study enrollment. The novel PLaCT risk classification score could divide MUO patients into three risk groups with distinct survival times and ureteral stent patencies. This score will aid in establishing prognosis and treatment strategy for all physicians engaged in cancer treatment.