Schizophrenia and bipolar disorder (BD) are psychiatric disorders with economic, social effects that cause disability. Treatment noncompliance is one of the major problems faced by clinicians in both schizophrenia and BD. Treatment non-compliance is associated with recurrence and impaired functionality. Treatment compliance increases with long-acting injectable antipsychotics (LAIAs) and recurrence times are prolonged, hospitalization rates decrease compared to those who use an equivalent oral form of the same drug. The use of LAIAs in the maintenance treatment of schizophrenia has also been associated with a low mortality rate, decrease in caregiver burden, and increase in patient satisfaction. Studies show that LAIAs are cost-effective compared to their oral forms. Data on the use of LAIAs in first-episode schizophrenia and BD are relatively limited. The results of studies on the use of LAIAs in patients with first-episode schizophrenia indicate that LAIAs are advantageous in preventing relapse and re-hospitalization compared to oral antipsychotics. In BD, with the use of LAIA, the rate of hospitalization due to mood episodes and the frequency of manic episodes have been decreased. LAIAs have not been found to be as effective in preventing depressive episodes in BD as manic episodes. Although there are many studies supporting the use of LAIAs in maintenance treatment of schizophrenia, more studies are needed on the use of LAIA in firstepisode schizophrenia and BD. In this article, studies on the use of LAIAs in schizophrenia, first episode schizophrenia and BD are reviewed and the place of LAIAs in treatment were discussed.