Risperidone is a potent antagonist of both dopamine (D2) and serotonin (5-HT2) receptors, demonstrating improvement of both positive and negative symptoms and a lower propensity for inducing extrapyramidal symptoms (EPS) than typical neuroleptics. Its most common side-effects, found in the Canadian multi-centre trial (Chouinard et al., 1993), were agitation, anxiety, insomnia, EPS, headache and nausea, in order of frequency. With regard to endocrine effects, risperidone causes an increase in prolactin levels similar to that of other neuroleptics (Claus et al., 1992). In open clinical trials (De Cuyper, 1991), the overall incidence of risperidone-induced endocrine side-effects was quite low: 2.9 % for amenorrhoea and 1-2% for galactorrhoea. However, it is assumed that the incidence can vary depending upon the characteristics of patients and the drug regimen, i.e. dosage and titration schedule. In our experience, hyperolactinaemia is likely to occur when prescribing risperidone to female or first-onset psychotic patients: we are reporting 5 cases of risperidone-induced hyperprolactinaemia with these characteristics.