Patients undergoing surgery for idiopathic scoliosis were studied to determine the incidence and aetiology of oliguria during the perioperative period and to evaluate the efficacy of low dose dopamine in preventing its occurrence. Thirty patients, aged 6–18 years undergoing elective surgery were studied. Anaesthesia was standardized. Patients were randomized to receive either dopamine infusion (3 μg·kg−1·min−1) (Group A) (n=15) or dextrose infusion (control) (Group B) (n=15). Serum and urinary electrolytes and osmolalities and serum antidiuretic hormone (ADH) concentrations were measured. Urine output and haemodynamic parameters were recorded. Intraoperative oliguria occurred in 7% of patients in Group A and 47% in Group B (P < 0.05). Postoperative oliguria occurred in 20% of patients in Group A and 47% in Group B (P > 0.05). Urine and serum biochemical analysis revealed a statistically significant decrease in serum sodium and osmolality (P < 0.005) and an increase in urinary sodium and osmolality in both groups. Serum ADH concentrations were increased in both groups (P < 0.05), returning to baseline 18 h postoperatively. We conclude that oliguria during corrective spinal surgery occurs in association with excess ADH secretion as opposed to perioperative hypovolaemia. Dopamine increases urine output in the perioperative period but does not prevent the release of ADH and its subsequent biochemical effects.