BACKGROUND Diuresis begins soon after renal transplantation. Although controversial, early post kidney transplant urine volume may correlate with favorable short- and long-term allograft survival. The aim of the present study was to examine the potential changes in urine volume within the first 6 months after renal transplantation. METHODS In a prospective study, the first month serum creatinine level and daily urine volume were measured at 24 and 48 hours, and at 1 month after renal transplantation in patients with stable kidney function without the evidence of allograft rejection (n = 54). Fifteen patients were also followed for their urine output at least 6 months post kidney transplantation. Data are expressed in mean values +/- SD. Statistical analysis was performed by SPSS version 13.0 using ANOVA. Correlation between continuous variables was performed using the Pearson test. The P value was set at .05. RESULTS The mean age of the renal allograft recipients was 35.5 +/- 12.1 years with a male to female ratio of approximately 1.3. The mean first month serum creatinine was 1.26 +/- 0.4 mg/dL. The mean urine outputs were 10.06 +/- 5.89, 5.45 +/- 3.05, and 3.44 +/- 1.25 L at 24 and 48 hours and 1 month post renal transplantation. Those patients who were followed for 6 months post transplant (n=15) were observed to have a mean urine volume of 3.20 +/- 1.24 L at the end of this period. This trend showed that urine volume steadily decreased from 24 and 48 hours to 1 month after renal transplantation (P<.05). However, urine volumes were rather comparable at one month and 6 months after transplantation (P>.05). A positive correlation was found between the first-month serum creatinine and the urine volume at one month (r=0.302 and P=.035). CONCLUSIONS Although urine volume showed considerable variation early after renal transplantation, it stabilized by 1 month after transplantation, which was also positively correlated with the first-month serum creatinine. Moreover, we concluded that in stable patients, the final urine output was related to early graft function.