Background: Some chemotherapy-naïve patients with locally advanced bladder cancer (LABC) after radical cystectomy (RC) are sufficiently de-conditioned that they are not candidates for adjuvant chemotherapy or decline it, even though such treatment may be warranted. There is no clear alternative adjuvant therapy for these patients, who are usually observed. In this study, we compare post-op radiotherapy (PORT) vs. adjuvant chemotherapy in a randomized clinical trial. We hypothesized that PORT can achieve comparable disease-free survival (DFS). Methods: A randomized phase III trial was opened to compare PORT vs. sequential chemo+PORT after RC for LABC & accrued from 2002–2008 at the NCI in Cairo. In 2007, a third arm comparing adjuvant chemo was added. Herein, we report the results of PORT vs. adjuvant chemo. Patients ≤70 y/o with ≥1 of the following factors (≥pT3b/T4a, grade 3, or positive nodes) with negative margins after RC + pelvic node dissection were eligible. Routine follow-up & pelvic CT q6 months were performed. PORT included 3D conformal pelvic RT (45Gy/1.5Gy BID). Chemo included gemcitabine/cisplatin x 4. Post-hoc non-inferiority exploratory analysis was performed. Results: The PORT arm accrued 78; the chemo arm accrued 45. 51% had urothelial carcinoma; 49% had squamous cell carcinoma/other. The two arms were well-balanced except for gender (p = 0.06). Two-year outcomes & overall adjusted hazard ratios (HR) for PORT vs. chemo alone were 54% vs. 47% (HR 0.65(95%CI 0.35-1.19, p = 0.16) for DFS; 92% vs. 69% (HR 0.28(95%CI 0.10-0.82), p = 0.02 for LRFS; 75% vs. 79% (HR 2.39(95%CI 0.94-6.09), p = 0.07) for DMFS; 61% vs. 60% (HR 0.94(95%CI 0.52-1.69), p = 0.83) for OS. Late grade ≥3 GI toxicity was observed in 6 PORT patients (8%) & 1 chemo patient (2%). Based on our data, there is a greater than 90% probability that the true difference in 2 yr DFS is less than 10%, the pre-specified non-inferiority margin. Conclusions: This randomized study demonstrates superior local control with PORT vs. adjuvant chemo with no significant differences in DFS, DMFS or OS. Results suggest that PORT could be an option for patients with LABC after RC who are medically unfit for adjuvant chemo or who decline it. Clinical trial information: NCT01734798