Summary Aim: 223Radium-dichloride (223Ra) administration is an upcoming therapeutic option in patients with castration-resistant metastatic prostate cancer (mCRPC), whose renal and faecal excretion of 223Ra has been primarily estimated from data of a phase-I clinical trial in patients with normal renal function. In the rare case of concomitant renal insufficiency requiring haemodialysis (HD), an estimation of the contamination of dialysate would be beneficial. Methods: The excretion of 223Ra and its concentration in the dialysate in a patient with mCRPC and end-stage renal disease was examined for six consecutive treatment cycles. Dialysate samples were measured using a commercial system with NaI-scintillation detector. Results: HD showed a residual activity level in the remaining dialysate. The excreted activity was a median of 46.1 kBq (range = 42.0 83.4 kBq) and 11.2 kBq (range = 8.419.9 kBq) for the first (24 h post injection p.i.) and second HD (96 h p.i.), respectively. The activity concentration decreased significantly from a median of 4.18 kBq/l (range = 2.98-5.14 kBq/l) to 0.85 kBq/l (range=0.69-1.31 kBq/l, p < 0.0001). For all consecutive time points, the activity concentration further decreased significantly (p < 0.0001). The activity concentration of dialysate from HD performed 125.4 h p.i. [95 % confidence interval = 120.5-130.4 h p.i.] reached the threshold for unrestricted waste disposal. Conclusion: The observed extraction of 223Ra by HD exceeded the data determined from the phase-I study. The activity concentration in the dialysate observed for the first HD’s p.i. was above the threshold for unrestricted disposal of radioactive waste in Germany. Therefore, the specific requirement for waste handling has to be followed to fulfil the radiation protection regulations.