The objective of this study was to assess the long-term safety and efficacy of olanzapine long-acting injection (LAI). A 6-year, single-arm, open-label extension study of olanzapine LAI was conducted at 127 sites in 25 countries. Patients were 18–76 years of age, were diagnosed with schizophrenia or schizoaffective disorder (N=931), and had been previously enrolled in one of three clinical trials of olanzapine LAI. Patients received flexibly dosed (45-405 mg) olanzapine LAI every 2–4 weeks. The mean duration of exposure was ∼3 years. A total of 393 (42.2%) patients completed the study. The mean weight change was +2.1 kg (P<0.001), with 40.6% of patients experiencing 7% or higher weight gain. Treatment-emergent categorical changes occurred in fasting glucose, total cholesterol, and triglyceride levels. Pharmacokinetic analyses revealed no systemic accumulation of olanzapine after long-term treatment. There were 36 occurrences of post-injection delirium/sedation syndrome, all resolving within 72 h. The mean Positive and Negative Syndrome Scale total and subscale scores did not change significantly over the course of the study, indicating clinical stability. Olanzapine LAI appeared effective as a long-term maintenance treatment, with a safety profile generally consistent with the known profile of oral olanzapine, except for injection-related events (including post-injection delirium/sedation syndrome).