Objectives: A small number of studies investigated the effects of lithium on biochemical parameters as maintenance therapy in children and adolescents. This study aimed to examine the effect of lithium on biochemical parameters. Materials and Methods: Electronic patient files and the follow-up of therapeutic lithium monitoring among patients who received lithium treatment for psychiatric disorders were retrospectively collected from the database of the biochemistry laboratory of the hospital. The blood lithium levels and biochemical findings of the patients receiving lithium treatment for more than 3 months and with a therapeutic drug monitoring more than twice were collected. Data concerning psychiatric disorders of the patients included were obtained from patient files. Results: Our findings did not suggest any significant changes in liver and kidney functions. At the 4th-8th months of the treatment, white blood cell and neutrophils counts increased compared to those in 16th-20th months of the treatment during which both decreased to normal levels. The white blood cell count and neutrophil doses in this period were significantly correlated with blood lithium levels. Similarly, creatinine and thyroid-stimulating hormone levels at the 8th-12th months of the treatment correlated with blood lithium levels. Conclusion: Our study results support that lithium might give rise to changes in laboratory parameters in the early stages of treatment. However, during the clinical follow-up up to two years, results have supported that lithium can be used in children and adolescents without any changes in biochemical parameters.