Background: Electronic collection of patient-reported outcomes (ePROs) is becoming widespread in health care, but the implementation into routine cancer care during therapy remains to be seen. Especially, little is known of the use and success of electronic reporting during active cancer treatment in fragile and comorbid patients. The aim of this study was to test the feasibility of ePRO and its incorporation into routine cancer care, measured by physician compliance, for a fragile and comorbid bladder cancer (BC) population receiving chemo- or immunotherapy. Methods: All BC patients initiating treatment for locally advanced or metastatic bladder cancer at Rigshospitalet or Herlev Hospital, Denmark, were approached during an 8 month period. Exclusion criteria were patients not speaking Danish or not being signed up for electronic communication with health authorities. Enrolled patients were prompted to complete weekly ePROs from home. Patients completed the European Organisation for Research and Treatment of Cancer's general quality of life questionnaire, QLQ-C30, and the module for muscle-invasive bladder cancer QLQ-BLM30, the Hospital Anxiety and Depression Scale, HADS, and selected items from the Patient Reported-Outcomes version of the Common Terminology Criteria of Adverse Events (PRO-CTCAE), in total 158 questions weekly. If failing to report when prompted, patients were sent two e-mail reminders. Patients were informed that the physician would have an overview of the reported ePROs at their following clinical visits. Physicians were at all clinical visits informed to look at the ePROs in a software solution separate from the medical records. Physicians were logged to check their compliance to the task. No continuous surveillance of ePROs was established. Results: Of 91 patients screened for enrolment, 19 patients (21%) were not found eligible for standard treatment, eight patients (9%) were not signed up for electronic communication with the health authorities and nine patients (10%) declined participation. Another six patients did not meet other inclusion criteria. In total 49 BC patients were enrolled, 29 initiating chemotherapy and 20 initiating immunotherapy. A total of 466 electronic questionnaires were completed. The overall adherence of the patients to complete ePROs was at an expected level for an elderly cancer population (75%) and remained above 70% until the 6th cycle of treatment. The physician' compliance was in contrast low (0-52%) throughout the course of treatment. Conclusions: Electronic reporting of PROs is feasible in a fragile and comorbid population of patients during routine active cancer treatment. Despite clear implementation strategies the physician compliance remained low throughout the study proving the need for further implementation strategies.