Haematological abnormalities are frequently encountered during treatment with antipsychotic drugs. Most of these are mild and of no clinical significance. In the case of many, there is often difficulty in establishing a cause-and-effect relationship between the drug and the abnormality. However, in a small minority of patients, hazardous, potentially life-threatening haematological effects can occur due to a combination of pharmacological and host factors. These include leucopenia and agranulocytosis. Although such effects are rare, it is essential that they are diagnosed and managed promptly. In this paper, the authors review the haematological adverse effects and safety of antipsychotic drugs and present a strategy for prevention.