Background: In 2012 the ALSYMPCA study established a 3.6 month Overall Survival (OS) benefit of mCRPC patients treated with Ra-223 over placebo. To date clinical outcomes of Ra-223 treatment in a non-study population have not been prospectively evaluated. Methods: The ROTOR registry aimed to include 300 patients in 20 Dutch hospitals prior to Ra-223 treatment at the physician’s discretion. Clinical parameters collected included: positioning of Ra-223, Adverse Events (AE’s; CTCAE v4.03), Skeletal Related Events (SRE) and survival data. SRE was defined as radiotherapy to a bone metastasis, a new pathological fracture, spinal cord compression and/or bone surgery. Progression-Free Survival (PFS) was defined as survival until radiological or clinical progression, subsequent treatment or death. Results: Between April 2014 and September 2017, 305 patients were included of whom 300 were evaluable. The mean age of patients was 72.6 (range 46.3-91.5) years, 255 (85%) had ≥ 6 bone metastases and 197 (65.5%) were pretreated with taxanes and/or abiraterone or enzalutamide (214 (71.3%)). Two-hundred and ninety (96.7%) patients were treated with Ra-223. Twenty-nine (9.7%), 104 (34.7%), 96 (32%) and 66 (22%) patients received Ra-223 as a first, second, third, ≥ fourth mCRPC treatment line, respectively. Patients received an average of 4.6 (SD 1.8) cycles of Ra-223, while 140 (46.7%) completed all six cycles. After a median follow-up of 13.2 months, PFS was 5.1 (CI 4.5-5.8) months and OS 15.2 (CI 12.8-17.6) months. Eighty-two (27.3%) patients were hospitalized during Ra-223 treatment (Serious AE). Grade ≥ 3 anemia, neutropenia and thrombocytopenia was found in 54 (18.0%), 8 (2.7%) and 11 (3.7%) patients, respectively. Other frequent AE’s (all grades) were nausea (90 (30%)), diarrhea (83 (27.7%)) and fatigue (178 (59.3%)). SREs were observed in 46 (15.3%) patients; 22 (7.3%) received radiotherapy, 6 (2%) developed pathologic fractures, 17 (5.6%) spinal cord compression and 1 (0.3%) received bone surgery during Ra-223 therapy. Conclusions: The non-study ROTOR population had characteristics, all grade AEs and OS comparable with the treatment arm of ALSYMPCA. Clinical trial information: NCT03223597