The present study reports clinical and laboratory data of patients with Bartter syndrome at diagnosis and follow-up with emphasis on the long-term benefits and side effects of the pharmacological therapy, which includes indomethacin and potassium supplementation. We followed 12 children, 6 boys, with a median age at diagnosis of 24.5 months (range 7-137 months) and at the end of the study 157.5 months (range 26.0-224.0 months). All children presented with polyuria and polydipsia, dehydration, and metabolic and electrolyte disturbances with failure to thrive. However, at study entry 5 of 12 patients also had hypophosphatemia, which disappeared after a mean time of 50+/-22.4 months, 3 of 12 had nephrocalcinosis, and 2 of 12 had typical renal cysts. Despite treatment, hypokalemia was persistent in some patients. During long-term follow-up we observed recovery of growth velocity and adequate metabolic and electrolyte balance. However, we noticed renal and gastrointestinal complications: 2 patients had a perforated gastric ulcer, 1 had a gastric ulcer, and gastritis was detected in 3 children. A decreased glomerular filtration rate was observed in 2 patients during follow-up. Our data emphasize the need for regular surveillance of renal function and gastrointestinal endoscopy in these patients. As an alternative to indomethacin, we present our satisfactory preliminary results with rofecoxib.