Objective The efficacy of oral hydration in the prevention of contrast-induced nephropathy in patients undergoing elective coronary intervention is unclear. Methods A total of 120 patients were randomly assigned to three groups. Group A (n = 40) received intravenous hydration before and after coronary angiography or angioplasty. Group B (n = 40) received oral tap water before and after the procedures, whereas group C (n = 40) received only post-procedural drinking water. Levels of serum creatinine and urea nitrogen were measured before, 12 hours after, 2 and 3 days after the coronary angiography or angioplasty. Results There was no statistically significant difference in the age, sex, baseline renal function and the volume of contrast medium used during the coronary procedures among the three groups (P > 0.05). There was no statistically significant difference in the mean serum creatinine or urea nitrogen among the three groups 12 hours, 2 and 3 days after the coronary procedures (P > 0.05). The incidence of contrast-induced nephropathy in group A, B and C was 5.0% (2/40), 7.5% (3/40) and 5.0% (2/40), respectively (P = 0.86). Renal function in the seven patients who experienced contrast-induced nephropathy recovered within a week following rehydration treatment. Conclusions Pre- and post-procedural oral hydration was as effective as intravenous rehydration in the prevention of contrast-induced nephropathy in patients undergoing coronary angiography or angioplasty.