Studies investigating the relationship between cigarette smoking and prolactin secretion in the general population have yielded inconsistent results. Many antipsychotic drugs increase prolactin secretion, but there are no published studies that have investigated the relationship between smoking and prolactinaemia in antipsychotic-treated patients. We obtained prolactin levels from 228 antipsychotic-treated patients in secondary care mental health services and investigated the relationship between prolactinaemia and cigarette smoking. Twenty-three percent (n = 52) of patients had hyperprolactinaemia. Patients prescribed typical or a combination of typical and atypical antipsychotics had a significantly higher prevalence of hyperprolactinaemia and higher mean prolactin concentration. Both current and ex-cigarette smokers had significantly lower mean prolactin levels and a lower prevalence of hyperprolactinaemia, but after controlling for potentially confounding variables, only current smoking status was a significant predictor of lower prolactin levels (OR 2.3, 95% CI 1.2 to 4.7, p = 0.002). In this preliminary, cross-sectional study, there was a robust statistical relationship between cigarette smoking and prolactinaemia. The mechanism(s) underpinning this association needs further investigation.