Background: Medication non-adherence is a common and significant public health problem, especially among the geriatric population. This study's objective was to measure medication adherence and associated factors among geriatric patients with chronic diseases. Methods: A cross-sectional study targeted outpatient geriatrics who suffer from chronic diseases at King Saud University Medical City (KSUMC), Riyadh, Saudi Arabia. Telephone interviews were utilized to collect data from participants using a structured questionnaire and the GMAS validated instrument scale (General Medication Adherence Scale) intended to measure important determinants impacting adherence: patient behaviour, cost, comorbidity, and pill burden. Results: A total of 422 patients were assessed for medication adherence. The Mean overall score for GMAS was 29.9±3.1 out of 33. (64.9%) of the patients had a high level of medication adherence. The patients had a high adherence on the domain of patient behavior related non-adherence (PBNA) (13.5±1.9) out of 15, a high adherence on the domain of additional disease and pill burden (ADPB) (11.2±1.4) out of 12, and good to high adherence on the cost-related non-adherence (CRNA) (5.25±1.1) out of 6. Conclusion:The geriatric population with chronic diseases in our study had a good level of adherence to medication if compared with other international figures. To promote better medication adherence, patients must have a good understanding of their disease and strong beliefs about the medications prescribed.