Subjects will be submitted to immediate-release methylphenidate treatment in a maximum dose of 0.5mg/kg/day. The total treatment monitoring is 06 (six) months, and patients will be evaluated at baseline, first, third and sixth month. The HUI rating scales are fulfilled by parents and patients (if >12 years old only) at baseline and 6th month. The period for inclusion of new patients comprises from 01/01/2011 to 31/12/2013.