This study was designed to test the hypothesis that non-ambulatory patients with spastic quadriplegia will have reduced bone mass which worsens with increasing age. Forty-eight patients (age 5 to 48 years, median age 15 years; 19 females and 29 males) were studied. Anticonvulsants were used in 29 patients (60.4%). Lumbar spine bone mineral density (LS-BMD) was markedly reduced compared with age-and sex-matched control individuals with a z score of -2.37 +/- 0.21. Twenty-eight (58%) had z scores of less than -2. A history of documented previous fracture was present in 19 patients (39%). Patients with a history of fracture had significantly lower (p = 0.05) LS-BMD z scores (-2.81 +/- 0.29) compared with those without a history of fracture (-2.11 +/- 0.26). Mean serum 25-OH vitamin D was 29.6 +/- 1.9ng/mL (normal 9 to 37.6ng/mL) with three patients having serum 25-OH vitamin D levels less than 15ng/mL. These findings indicate that BMD is markedly reduced in non-ambulatory children and adults with neuromuscular disease. Reductions in bone mass put them at greater risk for non-traumatic fractures.