Objectives: Hyperprolactinemia (HPRL), defined as plasma prolactin (PRL) >25 ng/ml, is a frequent adverse effect of the treatment with some antipsychotics. The objectives of this study were to determine the prevalence of HPRL among schizophrenic patients treated with long-acting injectable (LAI) antipsychotic drugs at our hospital, and to estimate gender effects in PRL levels in these patients. Methods: This cross-sectional, retrospective, study analyzed 165 psychotic patients treatment with LAI antipsychotics in monotherapy from February to May of 2017 at the Psychiatry Specialized Care Units of the Elche General Hospital (Spain). Results: The prevalence of antipsychotic-derived HPRL in our hospital was 52.41%. Patients treated with LAI formulations of paliperidone and risperidone presented the highest levels of HPRL. A linear regression model showed that female patients presented 24.95 ng/ml (CI95 = 16.85, 33.05) higher levels of PRL than male patients (p < .0001). For women, age >45 years was associated to reduced levels of PRL with respect to younger patients (mean= -18.86 ng/ml, CI95 = -35.59, -2.13, p < .05). Conclusions: Our study confirmed the effects of LAI paliperidone and risperidone on PRL levels. Sex and age were significantly associated with PRL levels in patients treated with LAI antipsychotics, with younger women presenting higher rates of HPRL than men. Key points HPRL is a common adverse effect of the treatment with antipsychotics, detectable in over half of the patients treated in our hospital. Our study showed that treatment with LAI formulations of paliperidone and risperidone resulted in the highest levels of HPRL. Sex and age were significantly associated with PRL levels in patients treated with LAI antipsychotic drugs, with younger women presenting higher rates of HPRL than men.