Background: External Beam radiotherapy is a standard treatment for patients with intermediate risk localised prostate cancer. Commonly the radiotherapy plan is delivered in two phases with adequate margins, the first phase to the prostate and seminal vesicles and the second phase to the prostate alone. The two phases can be delivered by intensity modulated radiotherapy as a sequential or concomitant treatment. We compared the toxicities and clinical outcomes of patients who received radiotherapy either as sequential or as concomitant treatment. Methods: Two hundred and twenty five consecutive patients with intermediate risk prostate cancer were included in the study. The patients who had sequential treatment received 60 Gy in 30 fractions to the prostate and seminal vesicles,, while patients who had concomitant treatment received 60 Gy in 37 fractions. All patients received 74 Gy in 37 fractions to the prostate. The Genitourinary (GU) and Gastrointestinal (GI) toxicity data and outcomes in terms of biochemical progression free survival were compared. Results: One hundred eighty patients received sequential radiotherapy, while forty five patients received concomitant radiotherapy. Acute GI toxicity was significantly less in the patients who received concomitant radiotherapy, during weeks four(p = 0.03), six(p = 0.03) and eight(p = 0.06) of treatment, compared to patients who receive sequential radiotherapy. Acute GU toxicities were similar in both groups of patients during treatment. Late GU and GI toxicity at 1 year and 2 years were similar. 3 year biochemical Progression free survival was 90 % for patients who received either sequential compared to 75 % for patients who received concomitant radiotherapy, though not statistically significant (log rank p value = 0.173). Conclusions: Concomitant radiotherapy to prostate and seminal vesicles resulted in lower acute gastrointestinal toxicity compared to sequential radiotherapy to the prostate and seminal vesicles as two phases. The genitourinary and late toxicities were similar. Biochemical progression free survival for patients who received concomitant radiotherapy treatment, could however be inferior to sequential treatment, probably due to the lower dose per fraction to the seminal vesicles and margins.