Background: A key difference between the landmark trials for docetaxel chemotherapy alongside ADT for mHSPC was the addition of prednisolone in the STAMPEDE but not CHAARTED or GETUG-AFU 15 trials, resulting in varied use in clinical practice. Potential toxicity from prolonged steroid use was recognised in a 2020 NHS England safety alert. This retrospective study compared toxicities in patients treated with docetaxel +/- prednisolone. Methods: Electronic notes of patients treated with docetaxel and ADT +/- prednisolone (per consultant preference) Feb 2018 - Sept 2020, were reviewed. Data was collected on common toxicities using CTCAE v5 grading. Analysis of incidence and severity were carried out using paired T-tests and logistic regression due to small sample sizes at each severity grade. Results: Data on 299 patients was collected; 167 received docetaxel and ADT, 132 also received prednisolone. There was no significant difference in the number of cycles completed between the 2 groups; 66.5% (no prednisolone) v 70.4% (with prednisolone) of patients completed 6 cycles (p=0.41). There was a significant difference in both the incidence and severity of anaemia between patients treated +/- prednisolone. There was no significant difference in the incidence of neutropenia or alopecia between patients treated +/- prednisolone, but prednisolone use was predictive of lower severity scores in neutropenia and alopecia. In contrast, there was a significant difference seen in incidence of neuropathy between the 2 groups, with no impact on severity. There was no significant difference in incidence or severity of thrombocytopenia, neutropenic sepsis, fatigue or nausea/vomiting. The prednisolone group had a significant increase in contacts with an advice hotline or general practitioner (p values <0.001). Review of interactions found many were requesting support with administration of prednisolone. Conclusions: These findings suggest limited clinical benefit in the addition of prednisolone to docetaxel and ADT in patients with mHSPC. Prednisolone is associated with significant potential harms e.g., impaired blood glucose and adrenal insufficiency (blood glucose was not routinely recorded in this group). These preliminary findings would benefit from further study with a larger sample size.