SUMMARY Background: Cancer of the prostate (CaP) is the most frequently diagnosed non-cutaneous malignancy worldwide and is the second leading cause of death from cancer in men. In our environment, majority of the patients with prostate cancer present with advanced disease and androgen deprivation therapy (ADT) is often the only treatment modality that can be offered to them. A number of studies have reported a high prevalence of osteopenia and osteoporosis in patients with CaP. Furthermore, treatment with ADT is known to be associated with reduced bone mineral density (BMD) and a higher risk of pathological fractures. Objectives: To determine the effects of advanced CaP and its treatment (using ADT) on BMD in patients with CaP. Patients and Methods: This was a prospective study conducted over 12 months between July 2016 and June 2017. The study population included case and control groups comprising: 77 patients with advanced CaP treated with ADT formed the case group while another set of 77 patients with benign prostatic hyperplasia formed the control group. The serum prostate specific antigen (PSA) and the BMD of the control group were measured on one occasion. Baseline measurement of the serum PSA of the case group was done prior to commencement of ADT and repeated 3 months post- ADT. The BMD of the case group was measured before initiating ADT and repeated 3 months post-ADT. Data analysis was done using SPSS version 22. Test of association was carried out using Chi square, Fischer’s exact test, Wilcoxon rank test, McNemar test, independent t-test, Man Whitney U-test and paired t-test as appropriate. For all statistical analysis, p-value < 0.05 (at 95% confidence interval) was considered as statistically significant. Results: The age of the patients ranged from 54 to 88 years (mean 70.15 ± 6.7) and 50 to 85 years (mean 68.92 ± 8.5) for the case and control groups respectively. The median PSA of the case group was 345.94ng/ml and 9.38ng/ml pre and post-ADT respectively (p<0.001). The median PSA of the control group was 3.89ng/ml. ADT was by bilateral orchidectomy in majority of the patients (70, 90.9%). The mean BMD of the control group (0.26 + 1.5) was significantly higher than that of the case group pre-ADT (- 0.78 + 1.7) with a p value of 0.044. The mean BMD of the case group was significantly higher pre-ADT (-0.78 ±1.7) than post-ADT (-1.15 ± 1.7) with a p-value of 0.001. There was no linear relationship between the Gleason score and the BMD. CONCLUSION: Advanced CaP was found to be associated with a decrease in BMD as evidenced by the significant difference between the mean pre-ADT BMD of the case group as compared to the BMD of the control group. In addition, ADT, which is the mainstay of treatment of advanced CaP was also associated with a decline in the BMD as evidenced by the significant difference in the mean BMD of the case group pre- and post-ADT.