Closed head injuries (CHI) may produce permanent, disabling changes in cognitive functions and social behaviour. Recent clinical case reports have suggested that stimulant medications may improve neurobehavioural functioning in CHI patients. In the present study, we evaluated the effects of methylphenidate (0-3 mg/kg b.i.d.) in 12 chronic CHI patients (14 to 108 months post-injury) using a double-blind, placebo-controlled, randomized, crossover design. Outcome measures consisted of cognitive tests of attention, learning and cognitive processing speed. In addition, a rating scale was completed by a close friend or relative to assess social behaviour. No significant differences were found between drug and placebo conditions on any of the neurobehavioural measures. These data do not support the clinical use of methylphenidate in the treatment of CHI patients.