Haemophilia care providers report anecdotally that many boys under their care bear the diagnosis of attention deficit hyperactivity disorder (ADHD). This study investigated the hypothesis that ADHD is over-represented among boys with haemophilia. All the boys with haemophilia, aged 5-14 years, who receive their comprehensive care at our centre were solicited to participate in this study. Of the 78 eligible boys, 34 (44%) were successfully contacted and agreed to participate. All participants were HIV-negative on both serological and PCR-based assays. The presence of ADHD symptoms was established via a parent- and teacher-completed standardized rating instrument. On the parent-rating scale, 26% of the participants exceeded the cut-off for inattentive ADHD, 18% for hyperactive/impulsive ADHD, and 18% for combined. On the teacher rating scale, 4% of the participants exceeded the cut-off for inattentive ADHD, but no participants were rated as having extreme hyperactive/impulsive or combined ADHD symptoms. Retrospectively, 29% of the participants had previously been diagnosed with ADHD, all treated with stimulant medications. Of note, 38% of our participants were enrolled in special education programmes. All of the above were more common in boys with haemophilia compared with national controls. A chart review of non-participating patients from the same clinic suggested that sampling bias is unlikely to account for these differences. These results provide the first empirical evidence that ADHD may be over-represented among boys with haemophilia.