Objective: Investigate the associations of long-acting injectable (LAI) second generation antipsychotic drugs with number of relapses, psychiatric admissions, days hospitalized, intentional self-harm events, and costs linked to hospitalizations in incident patients diagnosed with schizophrenia. Method: A nationwide, population-based, retrospective study utilizing mirror-image models before and after initiation of LAI SGA. Results: 10,509 patients were included as study population, with analyses being conducted on 2223 patients in a six-month period, 1383 in a 12-month period, 713 in a 24-month period. After initiation of LAI antipsychotics, patients experienced a reduction in number of relapses with an incidence rate ratio (IRR) of 0.60 for the first six months, IRR 0.64 for the first 12 months and IRR 0.64 for the first 24 months following initiation of LAI, all P < 0.001. The number of psychiatric admissions was reduced in a similar manner with respective IRR of 0.59, 0.60 and 0.64, all P < 0.001. Psychiatric bed-days were reduced with 58, 100 and 164 days for the respective periods after LAI initiation, all P < 0.001. In a Cox regression model in patients initiated on LAI, higher age at diagnosis, hazard rate ratio (HR) 0.99, 95%CI(0.98–0.99), P < 0.001, and a later calendar year of diagnosis, HR 0.99, 95%CI(0.98–1.00), P < 0.05, were associated with a lower risk of relapse, whereas mainly psychiatric comorbidity, HR 1.07, 95% CI (1.04–1.11), P < 0.001, and cardiovascular disease, HR 1.12, 95%CI(1.01–1.26), P < 0.05, were associated with relapse. Conclusion: Even though the design does not allow inferences regarding causality, these population-based findings support the use of second generation LAI antipsychotics.