OBJECTIVES: This study aimed to assess the medication adherence in patients with severe mental illness attending public tertiary care hospitals of Quetta, Pakistan. METHODS: A cross sectional study was conducted among the patients with severe mental illness attending public tertiary care hospitals (i.e. Bolan Medical Complex Hospital (BMCH) and Sandman Provincial Hospitals (SPH)) of Quetta, Pakistan. Morisky Medication Adherence Scale (Urdu version) was used for the data collection. The descriptive statistics was used to present the demographic characterization. Inferential statistics was used to the evaluation relationship among the study variables. All analyses were performed using SPSS 20.0. RESULTS: Out of all registered patients a total of 566 patients were agreed to participate and included in the study. The study population was dominated (n=330, 58.3%) by females. Majority of the respondent (n=151, 26.7%) belong to the age group 25-34 years. Having marital status as married (n=362, 63.9%) and occupation as house wife (n=321, 56.7%). A large population having (n= 449, 79.3%) no-education and have no-income 387 (68.4%). Majority (n=444, 78.4%) of the respondents were diagnosed with depression as major severe mental disorder, with disease duration of more than 2 years 375 (66.3%). Majority (n=324, 57.2%) of the patients were moderately adhere to the medication, while only 120 (21.2%) were of poor adherence.  CONCLUSIONS: The study result concluded that patient with severe mental illness was somewhat adhere to their medication. Effort should be made to improve the level of medication adherence so that patients get better treatment outcomes and live their normal life.