OBJECTIVE This study aims to assess the proportion of patients with schizophrenia or bipolar disorder who discontinued treatment with one of two oral formulations of olanzapine within 12 months in outpatient settings in Germany, Greece, and France. METHODS This 1-year, prospective, observational study included patients who had recently initiated treatment with olanzapine-coated tablets (OC) or the orodispersible (OD) formulation. Primary endpoint was olanzapine discontinuation for any reason. Clinical and functional status were also evaluated. RESULTS Out of 927 enrolled patients, 903 were included in the analyses (612 patients with schizophrenia, 291 with bipolar disorder). Within 12 months, 46 of 903 patients discontinued olanzapine. Most (95%) patients remained on olanzapine for 12 months with similar rates for patients with either diagnosis (94.5% for schizophrenia, 94.9% for bipolar disorder) and for both formulations (93.7% with OC, 95.3% with OD). The only factor significantly associated with time to discontinuation was baseline disease severity. Patients with more severe disease at baseline had a lower discontinuation risk. There were significant improvements in functioning and well-being and non-significant improvements in therapeutic alliance and compliance. CONCLUSIONS No significant difference was seen between discontinuation rates of the two formulations. Higher baseline severity was associated with a lower discontinuation rate.