BACKGROUND: 22q11 Deletion Syndrome (22qDS) is a genetic syndrome associated with various physical features and schizophrenia. Some reports have identified thrombocytopenia (platelet count < 150 x 10(9)/l) in individuals with 22qDS, especially children. We investigated whether adults with 22qDS and schizophrenia (22qDS-SZ) have lower platelet counts than other patients with schizophrenia (SZ). METHOD: Complete blood counts (CBC) were recorded from medical records for 18 22qDS-SZ and 60 SZ subjects. Five CBCs per subject were randomly selected and used to calculate a within-subject mean for analyses. RESULTS: 22qDS-SZ subjects had significantly lower mean platelet counts than comparison SZ subjects (142.2 x 10(9)/l versus 282.5 x 10(9)/l, t = -11.5, p < 0.0001). Ten 22qDS-SZ (55%) and no comparison subjects had thrombocytopenia. CONCLUSIONS: These results suggest that thrombocytopenia may be a common feature of 22qDS and that low platelet counts may comprise a readily available screening criterion to help identify this genetic syndrome among adults with schizophrenia.