The efficacy and acceptability of cinacalcet for treatment of secondary hyperparathyroidism (SHPT) was assessed in seven pediatric patients suffering from end-stage renal disease (ESRD) presenting with inadequately controlled SHPT despite conventional management. Patients received daily treatment with cinacalcet (dosage 0.25 mg/kg body weight) for a total of 4 weeks. Within 4 h after application of the first dose, median levels of serum parathyroid hormone (PTH) had decreased from 932 pg/ml (range 511-1,938 pg/ml) to 584 pg/ml (88-937 pg/ml), and final pre-dose values after 4 weeks were 199 pg/ml (121-940 pg/ml; each P < 0.05 versus baseline). Median concentrations of serum calcium (Ca) decreased within 4 h of the first administration, from 2.56 mmol/l to 2.38 mmol/l, returning to 2.58 mmol/l at 24 h, and they remained slightly decreased compared to baseline values thereafter (each P < 0.05 versus baseline). Both the median levels of serum phosphorus (P) and the Ca x P ion product decreased significantly during the 4-week period. Cinacalcet was well tolerated and without drug-related adverse effects. Thus, even with approximately half of the dose usually given to adult dialysis patients, PTH and the Ca x P ion product were markedly reduced in pediatric ESRD patients presenting with inadequately controlled SHPT. Therefore, our results support the initiation of a randomized, controlled, long-term trial in children.