Objectives: An open trial of pamidronate treatment was undertaken in 5 children and 4 young adults with polyostotic fibrous dysplasia associated with McCune Albright syndrome to assess clinical response, bone turnover, and cardiovascular status over a 2-year period. Study design: Pamidronate was administered by intravenous infusion 1 mg/kg/d for 3 days every 6 months for 2 years. Bone turnover was measured at 0, 6, 12, 18, and 24 months with bone mineral density, and cardiac output was assessed by echocardiography at 0, 12, and 24 months. Results: All subjects reported marked reduction in bone pain and sustained increased mobility. The fracture rate decreased in most. Orthopedic insertion of intramedullary rods was successful with maintenance of rod position. Mean osteocalcin levels fell from 35.5 ± 5.6 μg/L to 28.4 ± 4.1 μg/L (P <.03). Other bone turnover marker changes were not significant. The mean bone mineral density at lumbar spine increased from 0.5 ± 0.08 to 0.67 ± 0.03 g/cm² (P <.002) in children and 1.16 ± 0.6 to 1.33 ± 0.08 g/cm² in adults (P <.005). Other changes in bone mineral density were not significant. Cardiac output did not change significantly. Conclusions: Pamidronate treatment is an effective therapeutic modality for children with polyostotic fibrous dysplasia, with a good short-term safety profile. Failure to demonstrate major biochemical or bone densitometry improvements is due to the nature of the fibrous dysplasia and intercurrent microfracture. (J Pediatr 2000;137:403-9)