Described herein are methods and kits for prognosis of prostate cancer in a subject. The methods comprises: (a) determining the ratio of PCA3 and of a prostate-specific marker expression in a urine sample and (b) correlating the value of the PCA3/prostate-specific marker ratio with the aggressiveness and mortality risk of prostate cancer in the subject. Kits for prognosing prostate cancer are also described. More particularly, the present invention features a method for prognosing prostate cancer in a biological sample of a patient comprising: assessing the amount of a prostate cancer specific PCA3 mRNA and the amount of prostate-specific marker in the biological sample; determining a ratio value of this amount of prostate cancer specific PCA3 mRNA over the amount of prostate-specific marker; comparing the ratio value to at least one predetermined cut-off value, wherein a ratio value above the predetermined cut-off value is indicative of a higher risk of mortality of prostate cancer as compared to a ratio value below the predetermined cut-off value.