The present retrospective study aimed to determine the medication profile and estimate the treatment costs from medical records of new outpatients with schizophrenia, bipolar disorder, depression, and anxiety disorders from a healthcare perspective at a national referral hospital in Indonesia from 2016 to 2018. Methods: Medical records (including medical and administrative data) of 357 new outpatients with schizophrenia, bipolar disorder, depression, or anxiety disorders were collected from the hospital information system. The records of new outpatients with schizophrenia, bipolar disorder, depression, or anxiety disorders aged >18 years and had only received drugs for treatment were included. The medication profile was descriptively assessed, and estimated costs were calculated based on direct costs from a healthcare perspective. Results: Overall, 173 medical records were further analyzed. The main drugs administered to the new outpatients were atypical and typical antipsychotics for schizophrenia, atypical antipsychotics and mood stabilizers for bipolar disorder, antidepressants and atypical antipsychotics for depression, and antidepressants and benzodiazepines for anxiety disorders. The average annual treatment costs per patient were IDR 3,307,931 (USD 236) for schizophrenia, IDR 17,978,865 (USD 1,284) for bipolar disorder, IDR 1,601,850 (USD 114) for depression, and IDR 1,190,563 (USD 85) for anxiety disorders. Conclusion: The most commonly prescribed drugs for schizophrenia were haloperidol and risperidone; for bipolar disorders, sodium divalproex and risperidone; for depression, fluoxetine and sertraline; and for anxiety disorders, sertraline and lorazepam. Considering the high prevalence and estimated treatment costs for mental disorders, special attention is required to prevent an increase in their prevalence in Indonesia.