We investigated the outcome of patients with antenatally detected pelviureteric junction (PUJ) obstruction treated either conservatively or surgically. The series comprised 68 such patients, 54 with unilateral obstruction. Of the unilateral cases, 22 units were treated conservatively, 21 underwent early and 11 late surgery. Of the bilateral cases, 18 units were treated conservatively, 9 underwent early pyeloplasty, whereas 1 underwent later surgery. Among the conservatively treated unilateral cases, none of the patients' good renal function deteriorated during follow-up. In the group with early surgery, the primary good function remained unchanged in all. In some patients, moderate function improved after early pyeloplasty, but in patients with poor function no improvement occurred. Of patients who underwent late pyeloplasty, primary good renal function remained unchanged in all except 1, although it had deteriorated to moderate function in some before surgery. In all except 1 patient with bilateral obstruction treated conservatively, both the grade of hydronephrosis and split function remained unchanged. In most patients the outcome of antenatally detected unilateral PUJ obstruction with initially good renal function, whether treated conservatively or surgically, seems favorable. Some patients with moderate function might benefit from pyeloplasty. In kidneys with poor function, recovery may be minimal despite pyeloplasty.