BackgroundThere is recent evidence of some degree of shared genetic susceptibility between adult schizophrenia and childhood attention-deficit hyperactivity disorder (ADHD) for rare chromosomal variants.AimsTo determine whether there is overlap between common alleles conferring risk of schizophrenia in adults with those that do so for ADHD in children.MethodWe used recently published Psychiatric Genome-wide Association Study (GWAS) Consortium (PGC) adult schizophrenia data to define alleles over-represented in people with schizophrenia and tested whether those alleles were more common in 727 children with ADHD than in 2067 controls.ResultsSchizophrenia risk alleles discriminated ADHD cases from controls (P = 1.04 × 10⁴, R² = 0.45%); stronger discrimination was given by alleles that were risk alleles for both adult schizophrenia and adult bipolar disorder (also derived from a PGC data-set) (P = 9.98 ×10⁻⁶, R² × 0.59%).ConclusionsThis increasing evidence for a small, but significant, shared genetic susceptibility between adult schizophrenia and childhood ADHD highlights the importance of research work across traditional diagnostic boundaries.