['Multiple sclerosis is a chronic demyelinating disease rare in children. Currently marketed disease modifying therapies are limited to adults.', 'To determine the tolerability of interferon beta-1a (IFNB-1 a) 30 mcg injected intramuscularly once a week in children with clinically definite relapsing-remitting multiple sclerosis (RRMS).', 'A standardized questionnaire was sent to neurologists in the United States to determine the tolerability of IFNB-1 a in patients younger than 16 years.', 'Tolerability data were available for 9 of 33 children who were reported to initiate IFNB-1 a. Mean age on initiating treatment was 12.7 years (range 8 - 15) and mean duration of therapy was 17 months (range 5 - 36). No patient discontinued therapy due to an adverse event.'] Is interferon beta-1a in children with multiple sclerosis well tolerated?