Intramuscular injection of botulinum neurotoxin A is a relatively new method for treating spastic movement disorders in children. One major goal of any therapy for patients with movement disorders is to improve gross motor function. In this study, 18 patients with adductor spasm were treated with botulinum neurotoxin A. Treatment effect was determined with the Gross Motor Function Measure, a standardized, validated instrument designed to assist in assessment of gross motor function. Spastic muscle hyperactivity and joint mobility were evaluated by the modified Ashworth Scale and by range of motion, respectively. Compared to pretreatment values, significant improvement in gross motor function (P < .010), decrease in the modified Ashworth Scale, and increase in the range of motion (P < .010) were achieved. Patients with moderate impairment of gross motor function (classed at level III and level IV in the Gross Motor Function Classification System) benefited most from treatment. In patients with severe handicap (level V), only one of five treated patients showed improvement in gross motor function. Nevertheless, all patients in this subgroup benefited from improved ease in hygienic care. In conclusion, we have demonstrated that for most children with moderate functional impairment, the Gross Motor Function Measure is a useful instrument for objective documentation of improvements of gross motor function following treatment with botulinum neurotoxin A.