The investigation aimed to delineate the immediate effect of methylphenidate on decoding in the comorbid condition of attention-deficit/hyperactivity disorder and reading disorder. Boys with attention-deficit/hyperactivity and reading disorders (n = 25) between the ages of 7.9 and 11.7 years, with at least average intelligence and verbal processing abilities participated in a double-blind, acute, randomized, placebo-controlled crossover trial with a single dose of methylphenidate 0.3 to 0.4 mg/kg with weekly intervals between testing sessions. The test battery included tasks of attention/control functions and reading domain functions. Paired comparisons and first trial group comparison comparing performance under placebo and under methylphenidate were used. Methylphenidate selectively improved strategy/set shift (P = 0.004) and facilitated improvement both in rapid naming (P = 0.043) and word/nonword accuracy (P = 0.028/P = 0.035). These findings lend support to a possible influence of methylphenidate on cognitive attention functions related to reading skills in the comorbid group.