We reviewed 111 patients who presented with simultaneous renal calculi and a ureteropelvic junction obstruction. Of 34 patients with ureteropelvic junction obstruction and a coexisting struvite stone 62% had recurrent calculi. The use of antibiotics significantly affected the incidence of recurrent struvite calculi. In particular, if prolonged prophylactic antibiotics (greater than 3 months) were used 15% of the patients had recurrent stones, compared to 90% if only perioperative antibiotics (less than 15 days) were used (p < 0.001). Patients with ureteropelvic junction obstruction and coexisting nonstruvite calculi were treated by either observation alone (53) or metabolic evaluation with appropriate intervention (24). Metabolic evaluation of patients with nonstruvite calculi revealed that 76% had an identifiable metabolic abnormality, treatment of which significantly decreased the incidence of recurrent renal calculi: 17% of the patients on interventional therapy had recurrent stones compared to 55% treated by observation alone (p < 0.001).