OBJECTIVE: To validate a version of the Motor Function Measure (MFM) useful in neuromuscular children under 7 years old. DESIGN: Two prospective cohort study that documented the MFM completion of children aged between 2 and 7 years old. SETTING: French-speaking rehabilitation departments from France, Belgium and Switzerland. PARTICIPANTS: A total of 194 healthy children and 88 children with a neuromuscular disease participated in the study. INTERVENTIONS: Each patients where rated by the MFM either once or twice, with a delay between the two MFM ranging between8 and 30 days, by a trained medical professionals. MAIN OUTCOME MEASURE(S): Intra- and interrater reliability of the MFM. RESULTS: The subtests making up the MFM-32, a scale monitoring severity and progression of motor function in patients with a neuromuscular disease in 3 functional domains, were carried out in healthy children aged 2-7 years. Twenty items of the MFM-32 were successfully completed by these children and were used to constitute the MFM-20. Principal component analysis of the MFM-20 confirmed the 3 functional domains. Inter- and intra-rater reliability of the 3 sub-scores and total score were high (ICC > 0.90) and discriminant validity was good. CONCLUSIONS: The MFM-20 can be used as an outcome measure for assessment of motor function in young children with a neuromuscular disease.