The introduction of atypical antipsychotics into clinical practice has lead to an increase of adverse metabolic effects in psychotic patients. Amisulpride is a substituted benzamide derivative, and its use is associated with a lower risk of weight gain compared to other atypical antipsychotics. The case of an acute and excessive weight increase in a female first-episode schizophrenic patient who was treated with amisulpride monotherapy is reported. The improvement in psychopathology was remarkable. However, the patient gained 12.9 kg of body weight in the first 2 months of amisulpride administration and a total of 17.3 kg, 6 months after initiation of the treatment. Glucose and insulin levels, as well as a glucose tolerance test, remained normal throughout the observation period.